Indian Journal of Chemistry Vol. 438, Ju ly 2004, pp. 1499-1503

Synthesis of cyclophanes bearing 1,4-dioxabut-2-yne and 1,6-dioxahexa-2,4-diyne bridges and nanoscale cavities

Selhuraman Sankararaman,"* Manivannan Srinivasan," Vijay Narayanan" & Babu Vargheseb

' Department of Chemistry, Indian Institute of Technology, Chennai 600036, India . E-mail: sanka@iitm.ac. in

b Sophisticated Analyticallnstrumcnt Facility, Indian Institute of Technology, Chennai 600036, Indi a.

Received 21 April 2003; accepted (revised) 12 Jalluary 2004

Cyclophanes bearing bi sphenol-A, 3,3'-dinitrobisphenol-A and 4,4'-dihydroxybenzophenone as aromatic un its and 1,4-dioxabut-2-yne and 1,6-dioxahex a-2,4-diyne units as bridges have been sy nthesized. The cyc lophane from bisphenol-A bearing I ,4-dioxabut-2-yne bridges has been structurally characterized by single crystal X-ray crystallography and the cavity dimensions were obtained. The cavity dimensions obtained by sem iempirical calcul ations (AM I) indicate that these cyclo-phanes possess nanometer size cavities.

IPC: Int.CI.7 C 07 C 43/20

Shape-persistent macrocycles bearing acety lenic bridges have attracted much attention in the past dec-ade. 1 Among them, the ones that possess cavity of nanometer dimensions and have binding sites and func-tional groups inside or outside the cavity are impOltant in host-guest chemistry.2 The acetylenic un its as bridges impart rigidity to the macrocycle and the nu m-ber of acetylenic units in the bridge controls the size of the cavity of the macrocycle.3 The aromatic un it and the connectivity to the aromatic unit also playa major role in controlling the cavity dimensions of such mac-rocycles. Recently we had reported the synthesis and structures of isomeric cyclophanes bearing 1,4-dioxabut-2-yne and 1,6-dioxahexa-2,4-diyne units as bridges.4 These cyclophanes, possessing medium sized cavity, form donor acceptor complexes with electron acceptors such as tetracyanoethylene due to the elec-tron richness of the aren~ and the acetylenic units. Herein, we report the synthesis of cyclophanes with nanometer cavity dimensions. We also describe the synthesis of tetranitro derivatives of these cyclophanes and our attempts to convert them into cyclophanes bearing amino groups in the cavity. A comparison of the structure of one of the cyclophanes obtained from X-ray crystallography with the energy minimized structure from semiempirical calculations has been made.

Results and Discussion For the present study we have chosen bisphenol-A,

3,3'-dinitrobisphenol-A and 4,4'-dihydroxybenzo-

phenone as the aromatic units and 1,4-dioxabut-2-yne and 1 ,6-dioxahexa-2,4-diyne as the bridging units.

Cyc10phanes based on bisphenol-A. Bisphenol-A la and its dinitro derivative Ib were treated with buta-2-yne-1,4-diol ditosylate and the corresponding 1,4-dioxabut-2-yne bridged cyclophanes 2a-b were synthesized in a single step, albeit in very low yields (Scheme I). The cyclophanes were isolated and puri-fied by column chromatography and thoroughly char-acterized by spectroscopic data. The structure of 2a was determined by single crystal X-ray diffraction data (Figure 1). The calculated energy minimized structure of 2a obtained from semiempirical AM 1 calculations5 is shown in Figure 2. The cavity of the cyclophane can be approximated to a rectangular box and the cavity dimensions are 1.1 x 0.75 nm from the

Me

Me

OH

R

Me

Me R

OH

I'-==--~\

/ 0

R R

R R

0 \

2a 4.2% 2b 4.0%

\ 0

0 I

(a) TsO OT~ , K2C03 , acetone, reflux

Scheme I

Me

Me

1500 INDIAN J. CHEM., SEC B, JULY 2004

Figure 1- Structure of cyc lophane 2a in the crystal. The hydro-gen atoms are omitted fo r clarity.

Figure 2- Calculated (AM I) energy minimized structures of cyclophanes 2a (top) and 4a (bottom). The positi on of the oxygen

atoms and the cavity dimensions are indi cated.

crystal structure which are in good agreement with the calculated values of l.01 x 0.76 nm. In order to in-crease the dimensions of the cav ity to nanometer scale, synthesis of cyclophanes with 1,6-dioxahexa-2,4-diyne bridges was under taken. Propargylation of la-b using propargy l bromide in acetone using K2C03 proceeded in very good yields to g ive the correspond-ing bispropargyl derivatives 3a-b, respectively. Glaser-Eglinton coupling of 3a-b usi ng cupri c acetate gave the corresponding cyclophanes 4a-b, respec-tively, albeit in poor isolated yields (Scheme II). The

Me

Me

/

°

° \

R = H 3a 98 % R = N02 3b 95 % ! (b)

\

° R R

R R

° / R = H 4a 7.0 % R = N02 4b 4.5 %

(a) == CH2Br, K2C03 , acetone, reflux; (b) Cu(OAc)2.H20 , Py, ether, 90 °C

Scheme II

Me

Me

cyclophanes were isolated and purified by chromatog-raphy followed by recrystalli zation and characterized by spec troscopic data.

The IH-NMR spectra of cyclophanes 2a and 4a are nearly identical and cannot be readily distinguished. The aromatic protons appeared as AA'BB' pattern in both cases. However, they are readi ly distinguished from their 13C_NMR and mass spectroscopic data. Attempts to obtain single crystals of cyclophanes 4a-b suitable for X-ray crystallography were unsuccessful. However, the dimensions of the cavi ty were obtained from energy-minimized structure based on semi- em-pirical AMI calculations. The cavity dimensions for 4a are l.01 x 0.9 nm. Although the cavity dimensions reported fo r 2a and 4a approach nanometer scale, the cavities are still not large enough to encapsulate a C6(j molecule . Attempted encapsulation of C60, studied by 13C-NMR and UV-Vis spectroscopy,6 did not yield any positive indi cation of encapsulation. However, smaller e lectron acceptor, namely tetracyanoethylene formed colored charge transfer complex with 2a and 4a, as indicated by new absorpt ion bands O .. max = 395

SANKARARAMAN el af.: SYNTHESIS OF CYCLOPHANES WITH NANOMETER CAVITY DIMENSIONS 1501

and 535 nm in CH2Ch) in the Uv-Vis spectrum of a mixture of TCNE and the cyclophanes.7

Cyclophanes based on 4,4' -dihydroxybenzo-phenone. Using 4,4'-dihydroxybenzophenone 5 as the aromatic unit synthesis of cyclophanes bearing 1,4-dioxabut-2-yne bridging units was undertaken in a similar manner. Treatment of 5 with buta-2-yne-l,4-diol ditosylate in the presence of K2C03 gave cyclophane 6 (Scheme III). Inspite of the poor yield the cyclophane was isolated and fully characterized by spectroscopic data. Synthesis and crystal structure of the corresponding cyclophane from 5 bearing 1,6-dioxahexa-2,4-diyne bridging units has been reported by Vogtle. 8 Bispropargylation of 5 followed by coupling of the bis- propargyl derivative, according to the literature procedure, yielded the cOITesponding cyclophane bearing 1,6-dioxahexa-2,4-diyne as the bridging units whose spectroscopic properties were identical to the literature report. 8 However, in our hands the literature procedure yielded the cyclophane only in 2% as compared to 34% reported by the earlier workers.

Conclusion Cyclophanes based on bisphenol-A, 3,3'-dinitro-

bisphenol-A and 4,4'-dihydroxybenzophenone as the aromatic units bearing 1,4-dioxabut-2-yne (2a-b and 6) and 1,6-dioxahexa-2,4-diyne 4a-b as the bridging units have been synthesized. Attempted conversion of the tetranitro derivatives 2b and 4b to the correspond-ing aminocyclophanes was unsuccessful. Cycophane 2 has been structurally characterized by single crystal X-ray diffraction data from which the cavity dimen-sions were obtained. For the other cyclophanes the cavity dimensions were estimated from the calculated energy minimized structures based on semicmpirical AM I calculations. The cyclophanes reported herein possess cavities whose dimensions are in the nanome-ter scale.

Experimental Section General. 'H and I3C NMR spectra (CDCI3 solu-

tion) were recorded with a Jeol GSX-400 spectrome-ter at 400 MHz and 100 MHz or on a Bruker AM-200 at 200 MHz and 50 MHz, respectively; Chemical shifts are reported in ppm from TMS. Mass spectra were recorded either on a Finnigan MAT 8439 or a Finnigan MAT 8230 spectrometer. IR spectra were recorded either on a Nicolet 320 FfIR or on a Shima-dzu IR470 spectrometer. Column chromatography was performed on silica gel (60- 120 or 240-400

OH

o

OH

5

(al --. 1.0 %

Scheme III

o 6

mesh) with various mixtures of diethyl ether, ethyl acetate, and hexane. TLCs were run on Macherey-Nagel polygram sil G/UV254 plates. Melting points are uncorrected. 2-Butyn-l ,4-diol ditosylate9 and 3,3'-dinitrobisphenol-A '0 were synthesized according to the literature procedure and were characterized by spectroscopic data.

General method for the synthesis of 3a and 3b. Anhydrous K2C03 (18.2 g, 131.4 mmoles) was added to a refluxing solution of bisphenol A la (5.0 g, 21.9 mmoles) in acetone (150 cm3) with stirring. To this mixture, freshly distilled propargyl bromide (6.5 g, 54.7 mmoles) was added and reflux was continued for 22 hr. The reaction mixture was cooled to room tem-perature; solid K2C03 was filtered and washed with acetone. The combined washings was evaporated and the residue was diluted with CH2Cl2 (300 cm\ The organic layer was washed successively with water (3 x 200 cm\ saturated brine (200 cm3) and dIied over an-hydrous Na2S04. The crude product was chromatogra-phed on a short silica gel column and eluted with hex-ane-ethyl acetate mixture (19:1, v/v) to afford 3a as a colorless solid, 2,2-bis( 4-propargyloxyphenyl)propane 3a (6.54 g, 21.5 mmoles, 98%); mp 78-80 °C; IR (KBr): 3285,211 2 (C=C) , 2972, 1606 cm-'; 'H NMR (CDCb, 400 MHz) : 8 7.14 and 6.85 (8H, AA'BB' pattern , J = 8.79 Hz), 4.61 (4H, d, J = 2.4 Hz), 2.48 (2H, t, J = 2.4 Hz), 1.61 (6H, s); '3C NMR (100 MHz):

.8155.5 (s), 143.9 (s), 127.8 (d), 114.2 (d), 78.8 (s) 75 .4 (d), 55.8 (t), 41.8 (s), 31.0 (q); MS (70 eV, EI) mlz: 304 (M+, 30%), 289 (100); 2,2-bis(4-propargyloxy-3-nitrophenyl ) propane 3b (l1.7g, 95% from 31.4 mmoles of Ib); yellow needles, mp 99-100°C, IR (KBr): 3296,29 12, 1609, 1526 and 1344 (N02) cm-'; 'H NMR (COCl3, 400 MHz): 87.76 (2H, d, J = 2.44 Hz),

1502 INDIAN 1. CHEM., SEC B, JUL Y 2004

7.38 (2H, dd, J = 8.79 and 2.44 Hz), 7.21 (2H, d, J = 8.79 Hz), 4.83 (4H, d, J = 2.44 Hz), 2.61 (2H, t, J = 2.44 Hz), 1.71 (6H, s); 13C NMR (100 MHz) 8 149.1 (s), 143.0 (s), 139.8 (s), 132.6 (d), 123.5 (d), 115.5 (d), 77.23 (s), 77.17 (d), 57.2 (t), 42.1 (s), 30.4 (q).

General method for the synthesis of cyclophanes 2a, 2b and 6. To a solution of the bi sphenol deriva-tive (44.0 mmoles) in acetone (250 cm\ anhydrous K"C03 (36.3 g, 0.26 mole) was added and the mixture was refluxed for 0.5 hI'. To the mixture a solution of 2-butyne-1 ,4-diol ditosylate (19 .0 g, 48.2 mmoles) in acetone (50 cm3) was added drop wise over a period of 1 hI'. The resulting mixture was stirred and refluxed for 30 hr. The mixture was cooled and K2C0 3 was filtered and washed with acetone. The filtrate was concentrated under reduced pressure and the residue was dissolved in CH2Cb (200 cm\ The resulting so-lution was washed with water (2 x 200 cm3) and satu-rated brine (100 cm3) and the organic layer was dried over an hydrous Na2S04. Removal of solvent yielded a colorless solid . The crude product was chromatogra-phed on silica gel and eluted with hexane-ethyl ace-tate mixture 4: 1, v/v for 2a, 3:2, v/v for 6 and CH2Cb for 2b to afford the corresponding cyclophane as a crystalli ne solid.

2,7, 17, 22-Tetraoxa-12, 12,27, 27-tetramethyl-pen tacyclo[26.2.2.2(8, 11) .2( 13,16) .2(23,26)]octa triaconta-

1(30),8, 10, 13, 15, 23, 25,28,31,33,35, 37-dode-caene-4,19-diyne 2a : (0.51 g, 0.92 mmole, 4 .2%); colorless crystalline solid ; mp 230-32 DC; IR (KBr): 2928, 2899, 2868, 1602, 1504, 1469 cm' l; IH NMR (CDCI3, 400 MHz): 8 7.09 and 6.79 (16H, AA'BB/pattern, J = 8.86 Hz), 4.65 (8H, s), 1.67 (12H, s); I3C NMR (100 MHz): 8 155.1 (s), 143.9 (s), 127.5 (d), 114.5 (d), 83.0 (s), 55.6 (t), 41.6 (s), 30.9 (q); MS (70 eV, EI) mlz: 557 (20), 556 (M+, 55 %), 542 (35), 541 (100), 263 (24); HRMS exact mass : C38H360 -l requ ires 556.2608. Found: 556.26 13.

9, 15,24, 30-Tetranitro-2, 7, 17, 22-tetraoxa-12, 12,27,27 -tetramethylpentacyclo[26.2.2.2(8,11) .2(13,16). 2(23, 26)]octatriaconta-l(30), 8, 10, 13, 15, 23, 25, 28, 31, 33, 35, 37-dodecaene-4, 19-diyne 2b: (90 mg, 4.0% from 6.28 mmoles of Ib; yellow solid, mp 111-12°C; IR (KEr): 3456, 2960, 2336, 1612, 1529 and 1350 (N02) cm' l; IH NMR (CDCb, 400 MHz): 87.72 (4H, d, J = 2.44 Hz), 7.29 (4H, dd, J = 8.79 and 2.45 Hz), 7.08 (4H, d, J = 8.79 Hz), 4.84 (8H, s), 1.67 (12H, s); 13C NMR (100 MH~) : 8 149.0 (s), 143.1 (s), 139.8 (s), 132.7 (d), 123.5 (d) , 115.7 (d), 82.6 (s), 57.5 (t), 42.1 (s), 30.4 (q); MS (70 eV, EI) rnIz: 736

(M+), 686 (30), 540 (65), 318 (20) 303 (100), 172 (20), 91 (18).

2,7,17,22-Tetraoxapentacyclo[26.2.2.2(8,11).2(13,16). 2(23,26)]octatriaconta-l(30),8, 10, 13, 15,23,25,28,31, 33,35,37 -dodecaene-4,19-diyn-12,27 -dione 6: (37 mg, 1.0% from 14 mmoles of 5) ; white solid, mp >180 DC (decomposed); IR (KEr) 3456, 2928 , 1638 (C=O), 1600 cm'l; IH NMR (CDCb, 400 MHz): 8 7.35 (16H, AA'BB' pattern, J = 8.79 Hz), 4.82 (8H, s); 13C NMR (100 MHz):. 8 194.1 (s) , 160.6 (s), 132.0 (d), 131.3 (s), 114.5 (d), 82.44 (s) , 55.9 (t); MS (70 eV, El) rnIz: 528 (M+, 42%), 214 (52), 121 (100),93 (16), 65 (10); HRMS exact mass: C34H240 6 requires 528.1563. Found: 528.1573.

2,9,19,26-Tetraoxa-14,14,31 ,31-tetramethylpen-tacyclo[30.2.2.2(10,13) .2(15,18) .2(27,30)] diatetraconta-l (34),

10,12,15,17,27,29,32,35,37,39,41-dodecaene-4,6,21,23-tetrayne 4a. A solution of the bispropargyl ether 3a (5 .0 g, 16.44 mmoles) in ether (20 cm3) was added to a suspension of cupric acetate monohydrate (19.69 g, 98.64 mmoles) in a mixture of pyridine (375 cm3) and ether (125 cm3) at 90 DC with vigorous stirring over 3 hI'. The reaction mixture was cooled to room tem-perature and water was added (700 cm\ The mixture was extracted with CHCI3 (4 x 100 cm\ The com-bined organic extract was washed wi th ice cold 4 N HCI (3 x 100 cm\ saturated NaHC03 (2 x 100 cm\ water (200 cm3) and saturated bri ne (200 cm\ The organic layer was dried over anhydrous Na2S04 and filtered, and solvent was removed. The crude product was chromatographed on si lica gel and eluted with CH2Clz to afford a mixture consisting of cyclophane 4a and higher oligomers. This mixture was once again chromatographed on silica gel with hexane/ethyl ace-tate mixture (4: 1 v/v) to afford cyclophane 4a which was purified by recrystallization from a mixture of CH2Cb/hexane to yield pure cyclophane as a colou r-less solid (0.35 g, 0.59 mmole, 7.13%); mp 270 DC (decomposed); IR (KBr): 2976, 2928, 1603, 1504, 1027 cm' l; IH NMR (CDCI 3, 400 MHz): 87.08 and 6.79 (16H, AA'BB/pattern, J = 8.89 Hz), 4.66 (8H, s), 1.56 (12H, s); 13C NMR (100 MHz):. 8 155.2 (s) , 144.2 (s), 127.9 (d), 114.2 (d), 74.8 (s), 71 .1 (s), 56.0 (t), 41.8 (s), 31.0 (q); MS (70 eV, EI) rnIz: 604 (M+, 10%), 289 (11), 287 (10), 213 (95), 135 (100), 84 (38), 49 (50); HRMS exact mass: C42H360 4 requires 604.2613. Found: 604.2613; Analysis Calc. for C42H360 4 C, 83.40; H, 6.00. Found: C, 82.98; H, 5.98.

11,17,28,34-Tetranitro-2,9,19,26-tetraoxa-14,14, 31,31-tetramethylpcntacyclo[30.2.2.2(1o,l3) .2(15,18).

SANKARARAMAN el ai.: SYNTHESIS OF CYCLOPHANES WITH NANOMETER CAVITY DIMENSIONS 1503

2(27,30)]diatetraconta-l(34), 10, 12,15,17,27,29,32,35, 37,39,41-dodecaene-4,6,21,23-tetrayne 4b. Cyclo-phane 4b was synthesized from the bispropargyl ether 3b using the procedure described above for 4a. (45 mg, 4.5% from Ig, 2.5 mmoles of 3b, yellow solid, mp >152 °C (decomposed), IR (KBr): 3456, 2976, 1612, 1529 and 1353 (N02) cm-

I; IH NMR (CDCl3, 400 MHz): 87.75 (4H, d, J = 2.44 Hz), 7.36 (4H, dd, J = 8.79 and 2.44 Hz), 7.14 (4H, d, J = 8.79 Hz), 4.90 (8H, s), 1.70 (l2H, s); l3C NMR (100 MHz): 8 148.9 (s) , 143.3 (s), 139.8 (s), 132.7 (d), 123.6 (d), 115.5 (d), 73.9 (s), 72.1 (s), 57.7 (t), 42.2 (s), 30.5 (q).

Crystal data for compound 2a: C38 H36 0 4, M = 556.67, Monoclinic, space group P211c, a = 1 1.28(3), b = 10.626(3), c = 13.2371(19) A, a = 90, ~ = 102.59(6), Y = 90(7) deg. U = 1548(4) A3, T = 293(2) K, Z = 2, ~= 0.71073 A, m = 0.076 mm- I, 2856 reflections measured, 2711 unique (Rint = 0.0133), fina l wR(F2) [with 1>20'(1)] was 0.1044 and wR(F2) was 0.1190 (all data), refinement method was full-matrix least-squares on F2 and goodness of fit on F2 was 1.052. CCDC-203051 contains the supple mentary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc .cam.ac. uk/conts/retrievi ng.html [or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2IEZ, UK; Fax: (internat) +44-1223/336-033; email: deposit @ccdc.cam.ac.uk].

Acknowledgement Authors thank the Council of Scientific and Indus-

trial Research, New Delhi, for financial support and Prof. H. Hopf, Institute of Organic Chemistry, U ni-versity of Braunschweig, Germany for his constant support, encouragement and useful discussions. A graduate fellowship from lIT, Madras for MS is grate-fully acknowledged. Authors also thank the Sophisti-cated Analytical Instrument Facility, lIT, Madras for the spectral data.

References I For oxaarenccyc lynes: a) Yamaguchi Y, Kobayashi S, Amita

N, Wakamiya T, Matsubara Y, Sugi moto K & Yoshida Z. Telrahedron Lell .. 43, 2002, 3277. (b) Yamaguchi Y, Kobayashi S, Wakami ya T, Matsubara Y & Yoshida Z, J Alii Chelll Soc, 122, 2000, 7404. For phenylaccty lenc macrocyc les: c) Moorc J, Acc Chelll Res, 30, 1997, 402. Zhao D & Moore J, J Org Chem, 67, 2002, 3548.

For pyridine based macrocycles: e) Baxter P N W, Chelll EliI' J, 8, 2002, 5250. (f) Grave C & SchlUter A D, Eur J Org Chem, 2002, 3075. (g) Henze 0 , Lentz D, Schaefer A, Franke P & SchlUter A D, Chem EliI' J, 8, 2002, 357. (h) Tobe Y, Utsumi N, Nagano A & Naemura K, Org Lell, 2, 2000,3265 . For macrocyclic oligothiophenes: i) Fuhrmann G, Kromer J & Bauerle P, Syn Mela/s , 119, 2001 , 125. For porphyrin based ethynyl cyclophanes: j) Anderson S, Anderson H L & Sanders J K M, Acc Chell! Res, 26, 1993, 469. For giant cycles with acetylenic bridges: k) Godt A, Duda S, Onsal D, Thiel J, Harter A, Ross M, Tschierske C & Diele S, Chelll EliI' J, 8, 2002, 5094.

2 (a) Droz A S & Diederich F, J Chem Soc Perkin TrailS I , 2000,4224. (b) Droz A S, Neidlein U, Anderson S, Seilcr P & Dicderich F, Helv Chilli ACIa, 84, 2001 , 2243. (c) Fischer M & Hoger S, Eur J Org ClWII, 2003, 441.

3 For earlier reports on structurally re lated cyclophanes: a) O'Krongly D, Denmeade S R, Chiang M Y & Breslow R, J Alii Chelll Soc, 107, 1985,5544. (b) Friedrichsen B P & Whitlock H W, J Alii Chelll Soc, 111,1989,9 132. (c) Berscheid R, Niger M & Vogtie F, J Chelll Soc Chelll COl1ll11un, 1991 , 1364. (d) Vogtie F, Berscheid R & Schnick W, J Chem Soc Chelll COI11I11UII, 1991, 414. (e) Berscheid R & Vogtie F, Synlhesis, 1992, 58.

4 (a) Srinivasan M, Sankararaman S, HopI' H, Di x I & Jones P G, J Org Chel1l , 66, 2001 , 4299. (b) Srinivasan M, Sankararaman S, Hopf H & Varghese B, Eur J Org Chem, 2003, 660.

5 Calculations were performed using PC Spartan Pro Version I I , Wavefunction Inc, Irvine, CA.

6 The purple color of C60 in toluene generally changes to reddish brown upon complexation due to increase in thc absorbance in the region 400-500 nm in the Uv-Vi s spect rum For reports related to complexation of C60 see a) Yoshida Z el al in ref I a-b. (b) Tsubaki K, Tanaka K, Kinoshita T & Fuji K, J Chelll Soc Chelll COI/1I11UII , 1998, 859. (c) Kawase T, Ueda N, Tanaka K, Seirai Y & Oda M, Telrahedroll LeI!, 42, 2001, 5509.

7 Foster R, Charge Trallsfer COlllplexes, (Academic Press, New York) , 1969, Chapter 3.

8 Berscheid R, Nieger M & Vogtle F, Chell! Bel', 125, 1992, 2539.

9 (a) Brouard C, Pornet J & Mi giniae L, Synlhelic COI1lIllUII , 24, 1994,3047. (b) Ouchi M, Inour Y, Liu Y & Nagam usf S, BIIIl Chelll Soc JplI , 63, 1990, 1260.

10 (a) Long C -M, Sun H -Z, Tang 1, Liu H -S & Hu Y -C, Jillgxi HlIagollg, 19, 2002, 429; CA: 138, 108608. (b) Stronganov V F, Smirnov S P & Moshchinskaya N K, Zh Org Khilll1973, 171 3; CA: 79,126005.