identification and synthesis of elymniafuran, a new monoterpene from the butterfly elymnias...

FULL PAPER

Identification and Synthesis of Elymniafuran, a New Monoterpene from the Butterfly Elymnias thryallis Stefan Schulz*a, Mirjam Steffensky", and Yves Roisinb

Institut fur Organische Chemie, Universitat Hamburg", Martin-Luther-King-Platz 6, D-20 146 Hamburg, Germany Telefax: (internat.) +49(0)40/4123-3834 E-mail: [email protected]

Faculte des Sciences C. P. 160, Universite Libre de Bruxellesb, Avenue F. D. Roosevelt 50, B-1050 Bruxelles, Belgium

Received December 13, 1995

Key Words: Elymniafuran I Monoterpenes I Semiochemicals

The main constituent of the scent gland secretion of the tropi- furan (4) as well as the spiro acetal 3,9-dimethyl-l,6-dioxa- cal butterfly Elymnias thryallis (Lepidoptera: Satyridae) spiro[4.5]dec-3-ene (10). The structural assignment of these could be identified as (S)-2-methyl-l-(4-methyl-2-furyl)-3- new natural products as well as the synthesis and enantiome- buten-2-01 (elymniafuran, 3). It is accompanied by small ric separation by chiral gas chromatography are described. amounts of ( E ) - and (Z) -4 -methyl- (2 -methyl- 1,3 -butadienyl) -

Some species of the day flying satyrid butterflies use pheromones during courtship which was shown already by Tinbergen in his classical study of Hipparchiu semele[']. Since then, only the South East Asian species Lethe mar- ginulis was investigated chemically and 4-decanolide identified as the single compound present in male hindwing scent glandsL21. Elymnius thryullis is a satyrid butterfly found in Papua New Guinea which possesses a scent gland at the end of the abdomen. The butterfly secretes a fruity smelling fluid from this gland when bothered. The function of the gland is unknown; however, its secretion may act as deterrent against predators or even act as courtship pheromone. This paper describes the structural determination and the synthesis of secretion constituents which are needed for the establishment of the gland function.

Results and Discussion

The abdominal secretion of seven wild caught individuals was collected directly from the butterfly by absorption onto filter paper and investigated by GC and MS. The major compound A, accompanied by the trace constituents B, C, and D (see Figure l), exhibits a mass spectrum (see Figure 2) with prominent ions at mlz = 43, 71 (C4H70 determined by high-resolution MS), 95 (C6H70), and 96 (C6H80). The highest visible peak at rnlz = 166, presumably the molecular ion, has the composition of CIOH1402 (Mobsd. = 166.1063, Mcalcd, = 166.0994). Additonal information was obtained by microreactions of the secretion. Hydrogenation furnished a major compound E with a molecular ion at

156.1514), formed by hydrogenation of three double bonds and the hydrogenolytic loss of water. This compound was accompanied by small amounts of F, exhibiting a mass

m/Z = 156 (CIOH200, Mobsd. = 156.1467, Mcalcd. =

spectrum with ions at mlz = 154 and 157, presumably formed by loss of water or a methyl group from the molecular ion. Therefore, F had taken up three equivalents of hydrogen. A reaction with LiAlH4 did not alter the secretion.

Figure 1. Gas chromatogram of the scent gland secretion of Elym- nias thryallis

A

- min 20

From these data it was concluded that A might be a monoterpene, containing three double bonds and a hydroxy group. The prominent ion at mlz = 71 is characteristic of a

Liebigs Ann. 1996,94 1 - 946 0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1996 0947 - 3440/96/0606-O941 $ I 5.00+ .25/0 94 1

FULL PAPER S. Schulz, M. Steffensky, Y Roisin

Figure 2. Mass spectra of elymniafuran [A = (9-31, the natural furans B and C, the natural spiro acetal D (= lo), and the hydroge-

nation products E, F, and G

50

vinyl carbinol (shifted to mlz = 73 after hydrogenation to F). The ions at mlz = 95 and 96 can be explained by a- cleavage adjacent to a methylfuran ring and a McLafferty rearrangement. The mass spectra of E and F were domi- nated by base peaks at mlz = 85, arising from cleavage adjacent to the methyltetrahydrofuran ring. Therefore, compound A was proposed to be 2-methyl-I -(4-methyl-2-furyI)- 3-buten-2-01 (3), a previously unknown monoterpene which we called elymniafuran.

Structural verification was obtained by synthesis of rac- 3 starting from ruc-hotrienol (1). Oxidation with singlet oxygen according to ref.13] furnished the 1,2-dioxene rac-2, which could be converted into rac-3 by subsequent treat- ment with A1203 and acidL4]. The synthetic material shows an identical mass spectrum and gas chromatographic retention times on different stationary phases such as the natural A, thus proving our structural assignment to be correct.

Two trace constituents (B) of the secretion exhibit identical mass spectra (Figure 2). They were identified as the products of water elimination from 3, (E)- and (2)-4- methyl-2-(2-methyl-1,3-butadienyl)furan (4). Reaction of 3 with P0Cl3 in pyridine furnished a 1 : 1 mixture of the two isomers. Both compounds partly decomposed during purification by column chromatography using different adsorb-

Scheme 1. a: '02/CH2C12. - b: A1203/benzene. ~ c: H+/dioxane.

f 2 gf - b,c

- d: POClJpyridine

/

1 2

3 4

ents and thus could not be isolated in sufficient amounts for NMR spectroscopy. Therefore, the assignment of the stereochemistry of the trisubstituted double bond remains to be elucidated. Another trace constituent (C), 4-methyl- 2-(2-methylbutenyl)furan, contains only one double bond in the side chain with unknown position.

Compound D exhibits a molecular ion at mlz = 168 in its mass spectrum (see Figure 2). Prominent ions arise from loss of a methyl group (mlz = 153) or CH20 (mlz = 138), followed by a loss of methyl to furnish the base peak at mlz = 123. The hydrogenated product G took up one equiv- alent of hydrogen and shows the same losses of fragments as D (see Figure 2). Fragments formed by loss of CH20 are characteristic of bicyclic acetals, while the double peak at mlz = 98 and 101 in G is typical of spiro acetals. It arises from opening of the less stable ring and loss of the thus formed alkenyl group with preservation of one of the atoms adjacent to the spiro center, carbon (98) or oxygen (101)[51. Therefore, the more stable ring of G is either an unsubsti- tuted six-membered or a methyl-substituted five-membered ring. Ions arising from intact five membered rings predomi- nate under EI-MS conditions compared to ions containing a six membered ring15]. The low intensity of the correspond- ing pair at mlz = 11211 15 indicates another ring size in the less stable ring, thus pointing to a 1,6-dioxaspiro[4.5]decane system. The fact that only CH20 and no homolog is lost from M+ shows, that no substituent is located in a-position to the oxygen atoms. In spite of the monotcrpenoid nature of the secretion, compound G was proposed to be 3,9-dimethyl- 1,6-dioxaspiro[4.5]decane (8). The structural assignment was corroborated by base-catalyzed condensation of a mixture of 3-methyl-4-butanolide (5) and 3-methyl-5- hexanolide (6) according Thus, a mixture of spiro acetals with three different structures (7, 8, and 9) was obtained, of which one diastereomer of 8 shows the same mass spectrum and gas chromatographic retention time as G. The natural compound D contains an unsaturated five-membered ring, because the ion at mlz = 98 in G shifts to 96 in D. The double bond should be located between C-2 and C- 3, because in the other possible location between C-3 and C-4 elimination of CH20 from the molecular ion would be preventedL61. From these considerations we tentatively pro-

942 Liehigs Ann. 1996, 941 -946

Elymniafuran, a New Monoterpene FULL PAPER pose compound D to be 3,9-dimethyl-l,6-dioxapsiro[4.5]- dec-3-ene (10).

Scheme 2. a: NaOMe/MeOH

5 6

7 8 9

",I 10

Racemic 3 could be separated by gas chromatography using a chiral cyclodextrine as stationary and the natural compound proved to be a pure enantiomer. For the determination of its absolute configuration we needed an enantiomerically enriched synthetic sample of 3.

Our synthesis of 3 (see Scheme 1) allowed the preparation of such a sample by starting from enantiomerically enriched 1 instead of ruc-1. Racemic 1 can be obtained by addition of vinylmagnesium bromide to 6-methyl-4,6-heptadien-2- one[8]. An enantioselective variant can be devised with the method developed by Seebach and WeberL'], who used Grignard reagents in the presence of 4,5-bis(diphenylhy- droxymethyl)-2,2-dimethyldioxolane (TADDOL). While vinylmagnesium bromide reacted with 6-methyl-5-hepten-2- one in the presence of (4R,SR)-TADDOL to afford (S)-linalool with 6OYo ee in 45% yield, the same reaction with 6- methyl-4,6-heptadien-2-one was unsuccessful. Instead, the rearranged 6-methyl-3,5-heptadien-2-one was obtained, ob- viously formed under the strongly basic reaction conditions.

We therefore synthesized enantiomerically enriched 1 by modifying the method of Vig et al. for ruc-l['o] and starting from 3,3-dimethoxy-2-butanone (11). The chiral center was introduced by the enantioselective Grignard reaction of 11 with vinylmagnesium bromide in the presence of (4R,5R)- TADDOL. At - 78 "C (S)-5,5-dimethoxy-3-methyl-l- penten-3-01 (12) was obtained with 75% ee, but in low yield (4%) only. The main product proved to be 4-methoxy-3- buten-2-one which was formed by elimination of methanol. Performing the reaction at -50°C raised the yield to 49%, but the ee decreased to 30%. Nevertheless, this was sufficient to assign the absolute configuration of the natural compound. The nucleophile preferentially attacks from the re face in the presence of (4R,SR)-TADDOL['], thus for- ming (S)-12 as predominant enantiomer. Deprotection of 12 withp-toluenesulfonic acid as described by Vig et al. was

unsuccessful[l0I, leading to total destruction of the compound. Instead, the acetal was cleanly cleaved with tri- fluoroacetic acid at 0 "C. The resulting aldehyde 13 was converted into (9-1 by a Wittig reaction with (2-methyl-1-pro- peny1)triphenylphosphorane and potassium tert-butylate. To verify the re attack of the nucleophile on 11, the synthetic (9-1 was hydrogenated to yield (R)-tetrahydrolinalool [(R)-141 with an ee of 30%. Hydrogenation of (R)- linalool furnished (9-14, thus proving the correctness of the stereochemical assignment.

Scheme 3. a: CH2=CHMgBr, (4R,SR)-TADDOL, -40°C. - b: CF,COOH, 0°C. - C: (CH3),C=CHPPhi, KOtBu. - d: A120i/benzene. - e: H+/dioxane. - f H2, Pd/C

a p_p f l i M e - Me0 OMe CHO

11 12 13

/ 1 I A

14

Finally, (,S)-(l) was converted into (51-3 as described above by reaction with '02 followed by transformation of the dioxene 2 into (S)-3. The ee of 3 could be determined to be 30% by GC. Direct conversion of 2 into 3 was possible by reaction with Fe'"''], but the yield was lower (1 So/,). A gas chromatographic comparison between the scent gland secretion and the synthetic sample using a chiral cyclodextrine phase proved the natural compound to be the (S) enantiomer (see Figure 3).

The our knowledge the monoterpenes identified in E. thryullis have previously not been reported to occur in nature. Most furanoid monoterpenes contain substituents at C-3 (e.g. perillene, found in ants['']) or additionally at C-2 (e.g. rose furan, first identified as a constituent of verbena

Terpenoid 2,4-dialkylfurans are rarely encountered in nature. Examples are the sesquiterpene dehydrolasiosper- mane found in several plants[l4I as well as the related plera- ply~illine['~I and siphonodictidine['61 from marine organ- isms. Monoterpenes with a 2,4-dialkylfuran structure form a new class of natural products. Related compounds are the bicyclic menthofuran and its derivatives[l71, exhibiting a 2,3,4-trialkyl substitution pattern. The spiro acetal 10 is the first monoterpene with a 1,6-dioxaspiro[4.5]decane skel- eton. It may be formed from 3 by allylic transposition of the hydroxy group to the end of the alkyl chain, hydrogen-

Liehigs Ann. 1996, 941 -946 943

FULL PAPER S. Schulz, M. Steffensky, Y Roisin

Figure 3. Gas-chromatographic separations of synthetic 3 (A), natural (9 -3 (B), and a coinjection of the natural extract and the

synthetic sample (C)

A I

ation of one double bond, and additon to the furan ring. The only other known monoterpenoid spiro acetals are two diastereomers of 2,2,9-trimethyl-l,6-dioxaspiro[4.4]non-3- ene and their saturated analogs, isolated first from Ge- rnnium Interestingly, other dioxygenated monoterpenes such as (E)-2,6-dimethy1-6-octen-l,S-diol have been reported to be a constituent of pheromone glands of danaine butterflies["]. The related dioxygenated bishomoterpene (E,E)-3,7-dimethyldeca-3,7-diene-l, 10-diol acts as a glue for pheromone transfer particles which are transferred during courtship onto the females antennae in the danaine butterfly Dannus gilippus[20]. Further studies are needed to clarify the function of the furans identified in E. thryullis.

We thank Profs. W Fruncke (University of Hamburg) and M. Bopprt? (University of Freiburg) for helpful discussions, Dr. P Ack- ery (British Museum, London) for species determination, and Fir- nzenich s. A . for a gift of rue-1. Financial support by the DFG and the FCI as well as from the Belgium Fund for Basic Research (No. 2.9008.90) is gratefully acknowledged.

Experimental NMR: Bruker AMX 400 and Bruker AC 250-P, TMS as internal

standard. - MS: Fisons-Instrumcnts VG 70/250 SE and Fisons- Instruments MD 800. - Optical rotations: Perkin-Elmer 243 polar- imeter. - Column chromatography: Flash chromatography on silica gel (Merck, silica 60, 240-400 mesh). - Thin-layer chromatography: Merck, silica 60 F254. - Gas chromatography: Satochrom with split injector and flame ionization detector, hydrogen as car- rier gas. 30 m DB-5 fused silica column, Cr, = 0.32 pm. Analytical

enantiomer separations were performed on a 25 m fused silica column coated with a 1 : 1 mixture of heptakis(2,6-di-O-methyl-3-O- penty1)-P-cyclodextrine and OV-1701 as stationary phase. - Bio- logical material: Butterflies were caught in Papua New Guinea in the field and the secretion was collected immediately with a filter paper by gently pressing the abdomen. The filter papers were stored in pentane at low temperature until an analysis was carried out.

Microreuctions: Reduction with LiA1H4 was performed as described in ref.[2']. Hydrogenation: A mixture of 20 pl of a pentane extract of the secretion, 100 11 pentane, and a small amount of 5% Pd/A1203 was stirred under hydrogen (0.3 bar) in a 2-ml vial. After 2 h the mixture was filtered through a small cotton plug and the filtrate concentrated to a volume suitable for GC-MS analysis.

(S)-5,5-Dimethoxy-3-methyl-l -penten-3-01(12): According to the procedure of Seebach and WeberL9], a solution of (4R,SR)-TAD- DOL["] (14 g, 30 mmol) in 60 ml of anhydrous THF was cooled to - 70 "C, and 3 equiv. of a Grignard reagent, prepared from magnesium (2.88 g, 120 mmol) and vinyl bromide (13.9 g, 130 mmol) in anhydrous THF, were added in one portion. The reaction mixture was diluted with 50 ml of THF and allowed to warm up to room temp. After stirring for 15 min, the mixture was cooled to -50°C and a solution of freshly distilled 11 (3.0 g, 23 mmol) in 40 ml of THF added within 1.5 h. Stirring was continued for about 12 h while the solution slowly warmed up to - 10 "C. The reaction was quenched with a satd. solution of NH4C1 (100 ml), the organic layer separated, and the aqueous phase extracted three times with 60 ml of diethyl ether. After removal of the solvent from the combined extracts, the crude product was taken up in 100 ml of hexane and the solution was stored at 4°C for about 12 h. The solid thus obtained was removed by filtration and the filtrate concentrated in vacuo. Distillation of the residue afforded 1.8 g (@YO) of 12 enriched with the (S) enantiomer; b.p. 1 10°C/16 Torr, [a]? = -6.22 ( c = 8.5 in CHCI?), ee = 30% determined by gas chromatography. - 'H NMR (400 MHz. CDC13): 6 = 1.20 (s, 3H, 3-CH3), 1.76 (dd, J4,4 = 14.8 Hz, J4,5 = 4.3 Hz, 1 H, 4-H), 1.92 (dd, J4.5 = 8.5 Hz, 1 H, 4-H), 3.33 (s, 3H, OCH3), 3.34 (s, 1 H, OH); 3.36 ( s , 3H, OCH3), 4.54 (dd, l H , 5-H), 5.06 (dd, JI , , = 1.6 Hz, J I , ~ = 10.8 Hz, l H 1 I-H), 5.30 (dd, J1,2 = 17.2 Hz, l H , 1-H), 5.93 (dd, IH, 2-H). - 13C NMR (100 MHz, CDC13): 6 = 28.93 (3-CH3), 42.80 (C-4), 52.27 (OCH?), 53.52 (OCH3), 71.23 (C-3), 102.79 (C-5), 112.15 (C-l), 144.40 (C-2). - MS (70 eV): m/z (YO) = 145 (2) , 113 (22), 102 ( 5 ) , 101 (13), 97 (4), 96 (15), 95 ( 3 ) , 89 (3 ) , 87 (4), 85 (ll), 76 (9, 75 (IOO), 72 (5) , 71 (89), 69 (16), 68 (6) , 67 (9, 61 (7), 59 (39), 58 (76), 55 (52) , 47 (22), 45 (9, 43 (74), 42 (7), 41 (13), 39 (8). - C8HI6O3 (160.1): calcd. C 59.96, H 10.07; found C 59.76, H 10.01. - The yield of 12 decreased to 4% (ee = 75%) at a reaction temp. of -78 "C. The main product at this temperature was 4-methoxy-3-buten-2-one. 'H NMR (400 MHz, CDC13): 6 = 2.21 (s, 3H,

(d, 1 H, 4-H). - MS (70 eV): m/z (Yu) = 97 (3), 96 (29), 95 (4), 81 (53) , 67 (2) , 54 (3, 53 (loo), 51 (14), 43 (40), 39 (10).

1-H), 3.48 (s, 3H, OCH3), 5.52 (d, J3,4= 12.0 Hz, l H , 3-H), 5.60

(S)-3-Hydroxy-3-methylpent-4-enal(13): To a stirred solution of 12 (1.5 g, 9 mmol) in 25 ml of chloroform 25 ml of 50% trifluoro- acetic acid was added at 0°C according to The reaction progress was monitored by GC. After 13 h 50 ml of a satd. sodium hydrogencarbonate solution was added, the organic layer separated and dried with magnesium sulfate. The solvent was evaporated in vacuo and the crude product (970 mg, 95%) used in the following reaction without further purification. - 'H NMR (400 MHz, CDC13): 6 = 1.25 (s , 3H, 3-CH3), 2.33 (dd, J1,2 = 2.0 Hz, J2.2 = 16.4 Hz, l H , 2-H), 2.38 (dd, l H , 2-H), 5.17 (dd, J4.5 = 16.6 Hz, J5.5 = 0.8 Hz, l H , 5-H), 5.40 (dd, J4,5 = 10.8 Hz, l H , 5-H), 5.95

944 Liebigs Ann. 1996, 941-946

Elymniafuran, a New Monoterpene FULL PAPER (dd, 1 H, 4-H), 9.70 (t, 1 H, 1-H). - MS (70 eV): m/z ('$6) = 99 (4), 96 (41, 95 (31, 81 (31, 72 (8), 71 (71), 70 (13), 69 (6), 68 (17), 67 (lo), 57 (41, 55 (66), 53 (1% 51 (4), 44 (23), 43 (loo), 42 (13), 41 (23), 40 (15), 39 (15).

( S ) -3,7-Dimethyl-1,5,7-octatrien-3-ol [ ( S ) - Hotrienol, ( S ) -11: The necessary Wittig salt (2-methyl- 1 -propenyl)triphenylphosphon- ium chloride was prepared by boiling a mixture of freshly distilled l-chloro-2-methyl-2-propene (25 g, 0.27 mol), triphenylphosphane (50 g, 0.19 mol), and 50 ml of dry toluene for 48 hcZ41. The crude product was purified by column chromatography on silica gel (100 g). After elution of excess triphenylphosphane with diethyl ether, the Wittig salt (51 g, 74%) was isolated with ethanol. ['H NMR

7.62-7.91 (m, 15H, Ar). - 13C NMR (100 MHz, CDC13): 6 = 60.86 (2 C-3), 130.75 (C-2), 133.58 (C-l).] A suspension of this salt (2.01 g, 5.9 mmol) in 100 ml of absolute THF was cooled to -5"C, potassium tert-butylate (718 mg, 5.9 mmol) added in small portions and the mixture stirred for 15 min. After the resulting ylid solution had been cooled to -4O"C, a solution of 13 (331 mg, 3.0 mmol) in THF (20 ml) was added dropwise over 20 min and stirring continued for 1 h. The reaction mixture was poured into 80 ml of ice- cold water and extracted three times with diethyl ether. The combined organic layers were washed with brine and dried with magnesium sulfate. After evaporation of the solvent, the semicrystalline residue was taken up in hexane and the solution stored at 0°C for 6 h. The solid thus obtained was removed by filtration, the filtrate concentrated in vacuo and the residue subjected to flash chromatography on silica gel (hexane/ethyl acetate, 2.1) to give 220 mg (48%) of (9-1, predominantly as the ( E ) isomer. Colorless oil, ee = 28 k 2%, determined by GC, [a]g = +3.1 (c = 4 in CHC13). - 'H

7-CH3), 2.35-2.47 (m, J4,4 = 6.8 Hz, J4,5 = 7.2 Hz, 2H, 4-H), 4.87-4.98 (m, Jx,xt = 6.1 Hz, 2H, 8-H), 5.08 (dd, = 2.7 Hz,

5.63-5.72 (m, = 16.0 Hz, l H , 5-H), 5.97 (dd, l H , 2-H), 6.25 (d,

(400 MHz, CDC13): 6 = 1.64 (s, 6H, 3-H), 6.75 (d, lH , I-H),

NMR (400 MHz, CDC13): 6 = 1.31 (s, 3H, 3-CH3), 1.85 (s, 3H,

JL,2 = 10.8 Hz, IH, 1-H), 5.18 (dd, J1',2 = 17.2 Hz, 1 H, 1-H),

l H , 6-H). - 13C NMR (100 MHz, CDC13): 6 = 18.64 (7-CH3), 27.30 (3-CH3), 45.77 (C-4), 72.81 (C-3), 111.99 (C-l), 115.58 (C- 8), 124.87 (C-5), 137.03 (C-6), 141.75 (C-7), 144.77 (C-2). - MS (70 eV): ndz (%) = 119 (3), 109 (2), 105 (3), 91 (6), 83 (4), 82 (42), 81 (4), 79 (7), 77 (5 ) , 72 (4), 71 (loo), 67 (23), 66 (3), 65 (4), 55 (9),

calcd. C 78.89, H 10.51; found C 78.64, H 10.30. 53 (7), 44 (4), 43 (27), 41 (lo), 40 (lo), 39 (8). - CIOH160 (152.2):

(2's) -3- (2-Hydroxy-2-methy1-3-butenyl) -S-methyl-1,2-diox-4-ene (2): According to ref.L3], a mixture of (9-1 (220 mg, 1.5 mmol) and rose bengal (sensitizer, 12 mg) in 50 ml of dichloromethane and 5 ml of methanol was irradiated with a 400-W mercury vapor lamp while oxygen was bubbled through the reaction mixture. The lamp was cooled with a borosilicate glass water jacket, thus excluding the UV radiation. After 28 h analytical TLC showed complete reaction. The solvent was removed and the crude product purified by flash chromatography on silica gel (hexane/diethyl ether, 3:2) to give 212 mg (78%) of a 1 : 1 mixture of the two diastereomeric endo- peroxides 2.

First eluting diastereomer: 'H NMR (250 MHz, CDC13): 6 =

1-H'), 1.68 (br. s, 3H, 4-CH3), 2.01 (dd, J l t ,3 = 10.2 Hz, l H , 1- H'), 2.81 (br. s, l H , OH), 4.32 (bd, J6,6 = 16.0 Hz, l H , 6-H), 4.38 (bd, l H , 6-H), 4.70 (m, J3,4 = 6.6 Hz, lH , 3-H), 5.13 (dd, J4s,4s =

4-H'), 5.48 (m, J = 1.0 Hz, J = 0.4 Hz, 1 H, 4-H), 5.89 (dd, 1 H, 3-H'). - CI0Hl6O3 (184.2): calcd. C 65.19, H 8.75; found C 64.97, H 8.65.

1.28 (s, 3H, 2'-CH3), 1.67 (dd, J1,,l, = 15.2 Hz, J1,,3 = 2.6 Hz, l H ,

1.4 Hz, J3r.4, = 10.6 Hz, 1 H, 4-H'), 5.35 (dd, J4,,3' = 17.2 Hz, 1 H,

Second eluting diastereomer: 'H NMR (270 MHz, CDCl,): 6 =

1.36 (s, 3H, CH3-2'), 1.70 (br. s, 3H, 5-H), 1.73 (dd, JI,,) = 3.6 Hz,

4.37 (br. s, 2H, 6-H), 4.75 (m, l H , 3-H), 5.07 (dd, J4r,4r = 1.4 Hz,

5.57 (m, J = 1.0 Hz, l H , 4-H), 5.96 (dd, lH , 3-H'). - CI0Hl6O3 (184.2): calcd. C 65.19, H 8.75; found C 65.08, H 8.79.

Jj,,l, = 15.0 Hz, l H , 1-H'), 1.94 (dd, J1 , ,3 = 8.6 Hz, l H , 1-H'),

J3,,4, = 11.0 Hz, l H , 4-H'), 5.26 (dd, J3,,4, = 17.2 Hz, l H , 4-H'),

Elymniafuran [ ( S ) -2-Methyl-1- (4-methyl-2-firryl)-3-buten-2-ol, (8-31: A solution of (59-2 (100 mg, 0.54 mmol) in benzene (1 ml) was added to A1203 (3 g Woelm alumina B, activity 1) and left for 2 h at room temp. with occasional shaking as described in ref.I41. The mixture was filled into a glass column and the product eluted with methanolldiethyl ether (4:1, 40 ml). After removal of the solvent, the crude product was dissolved in 8 ml of dioxane and the solution stirred for 45 min with 0.1 g of p-toluenesulfonic acid. Then potassium hydrogen carbonate (1 g) and water (4 ml) were added and stirring was continued until the evolution of gas ceased. The resulting mixture was extracted three times with diethyl ether, the combined organic phases were dried with MgS04, the solvent was removed and the crude product purified by column chromatography (hexane) yielding a colorless oil of 95% purity (38 mg, 22 mmol, 42% yield). Repeated chromatography on different adsorb- ents did not yield a product with higher purity. - [a]g = 9.5 f 2 (c = 0.2 in CH,CI,). - 'H NMR (400 MHz, CDC13): 6 = 1.35 (s, 3H, 2'-CH3), 1.95 (bd, J = 1.2 Hz, 3H, 4-CH3), 2.89 (br. s, 2H,

(dd, J3,,4f = 15.8 Hz, l H , 4'-H), 6.02 (br. s, lH, 3-H), 6.05 (dd, 1'-H), 5.14 (dd, J3,,4, = 9.6 Hz, J4,,4' = 1.2 Hz, l H , 4'-H), 5.45

l H , 3'-H), 7.10 (t, J = 1.2 Hz, 1 H, 5-H). - 13C NMR (100 MHz, CDC13): 6 = 9.75 (CH3-C-4), 27.39 (CH3-C-2'), 41.16 (C-l'), 72.64 (C-2'), 110.84 (C-3), 112.04 (C-4'), 120.54 (C-4), 130.32 (C-5), 144.22 (C-3'), 151.82 (C-2). - MS (70 eV): See Figure 1. - Cl0Hl4O2: calcd. 166.0994, found 166.1 157 (MS). - Alternatively, compounds 2 were converted into 3 by reaction with FeS04 . 7 H 2 0 in acetone according to ref.["], resulting in 15% yield of the product.

4-Methyl-2-(2-methyl-l,3-butadienyl) furan (4): A mixture of 3 (20 mg, 0.12 mmol), P0Cl3 (0.5 ml) and pyridine (2 ml) was stirred for 1 d at room temp. This mixture was extracted 5 times with pentane, the combined organic phases were washed with water and a satd. sodium hydrogen carbonate solution. The product was separated by column chromatography on deactivated silica (hexane/ diethyl ether, 4: 1). During this operation part of it detoriated. The resulting 1 : 1 mixture of regioisomers was investigated by GC-MS. MS (70 eV): See Figure 1. - CIOHl20: calcd. 148.0888, found 148.0892 and 148.0893 (MS).

Tetrahydrolinalool (3,7-Dimethyl-3-octanol, 14): A solution of (R)-linalool (10 mg, 0.065 mmol) in ethanol was hydrogenated with a small amount of 10% Pd/C as catalyst. After filtration and removal of the solvent, pure (8-14 was obtained. In a similar experi- ment, the synthetic (9-1 furnished (R)-14 with an ee of 30%. The enantiomers of 14 were analysed by gas chromatography on a chiral cyclodextrine phase. Retention times: 9.95 min [(9-14] and 10.20 rnin [(R)-14]. - 'H NMR (400 MHz, CDC13): 6 = 0.86 (d, J7,x =

CHI), 1.27-1.44 (m, 6H, 4-, 5-, and 6-H), 1.48 (q, 2H, 2-H), 1.51-1.60 (m, lH , 7-H). - I3C NMR (100 MHz, CDC13): 6 =

(70 eV): ndz (YO) = 143 (l), 129 (3, 111 (S), 85 (l), 84 (l), 83 (6), 74 (6), 73 (loo), 71 (6), 70 (12), 69 (66), 67 (2), 59 (3), 58 (9, 57 (lo), 56 (9, 55 (45), 53 (3), 45 (l l) , 44 (l), 53 (52), 41 (31), 39 (10).

6.6 Hz, 6H, 8-H), 0.90 (t, J1.2 = 7.6 Hz, 3H, 1-H), 1.14 (s, 3H, 3-

8.21, 21.62, 22.63, 26.41, 27.98, 34.27, 39.60, 41.61, 72.98. - MS

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identification and synthesis of elymniafuran, a new monoterpene from the butterfly elymnias...

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