ch. 23 - introduction to organometallic...

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ORGANIC - KLEIN 3E

CH. 23 - INTRODUCTION TO ORGANOMETALLIC COMPOUNDS

CONCEPT: PREPARATION OF ORGANOMETALLICS

□ Organometallics are alkylating agents that have mostly group IA or group IIA metals bonded to a carbon structure

● They can also react as strong ____________. Beware of cross-reactions with acidic hydrogens.

1. Sodium Alkynides

2. Grignard Reagents

3. Organolithium Reagents

4. Gilman Reagents

ORGANIC - KLEIN 3E


CONCEPT: REACTIONS OF ORGANOMETALLICS

1. Substitution/Elimination on Alkyl Halides

2. Nucleophilic Addition on Ketones and Aldehydes

3. Nucleophilic Acyl Substitution on Esters

4. Base-Catalyzed Epoxide Ring Opening

ORGANIC - KLEIN 3E


CONCEPT: USE OF PROTECTING GROUPS

□ Organometallics are powerful bases. They will react with any acidic protons available, ruining the reagent.

We can use tert-butyl or silyl ethers to protect alcohols from deprotonation by organometallic reagents

● p-Toluenesulfonic acid is an acid commonly used for this step (abbrev. TsOH or pTSA)

EXAMPLE: Provide the mechanism and final product for the following transformation

ORGANIC - KLEIN 3E


PRACTICE: Predict the product of the following reaction.

ORGANIC - KLEIN 3E


PRACTICE: Propose a synthesis to accomplish the following transformation.

ORGANIC - KLEIN 3E


PRACTICE: Propose a synthesis to accomplish the following transformation (Hint: 4 steps)

ORGANIC - KLEIN 3E


CONCEPT: ORGANOMETALLICS

1. Nucleophilic Addition on Ketones and Aldehydes

EXAMPLE: Show the mechanism and predict the product for the following reaction.

ORGANIC - KLEIN 3E


PRACTICE: Provide the major product for the following reaction.

ORGANIC - KLEIN 3E


PRACTICE: Provide the major product for the following reaction dealing with the Grignard reagent.

Br

Mg

Ether (ROR)

O

H3O+

ORGANIC - KLEIN 3E



ORGANIC - KLEIN 3E



Br

OH

TMS-Cl

N(Et)3

A

Mg

Ether (ROR)

O

H3O+

B C

ORGANIC - KLEIN 3E


CONCEPT: KETONES FROM NITRILES

Nitriles can act very much like carbonyl compounds when exposed to a strong Nu- like a Grignard

Mechanism:

ORGANIC - KLEIN 3E


CONCEPT: KETONES FROM ACID CHLORIDES

When a good leaving group is present on a carbonyl, organometallics tend to react twice, yielding disubstituted alcohols.

Nucleophilic Acyl Substitution on Esters and Acid Chlorides

From Acid Chlorides:

We can reduce the power of the organometal by using a Gilman to yield _________ from RCOCl

□ This reagent stops after the first nucleophilic addition

ORGANIC - KLEIN 3E


PRACTICE: Provide the major product for the following reaction.

Cl

O

(CH3CH2)2CuLi

Ether

ORGANIC - KLEIN 3E


CONCEPT: CYCLOPROPANATION

□ Carbenes are reactive intermediates. They are unstable because they violate the ___________ ___________.

□ There are 4 methods commonly used to introduce carbene intermediates:

1.

2.

3.

4.

ORGANIC - KLEIN 3E


ch. 23 - introduction to organometallic...

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