Publication

A New Stereoselective and Convergent Approach to the Synthesis of Long-Chain Polypropionate Fragments

Pierre Vogel
1994
Journal Articles

Abstract

Optically pure Diels-Alder adducts of 2,4-dimethylfuran and 1-cyanovinyl (1'R)- or (1'S)-camphanate are obtained readily. These 1,5-dimethyl-7-oxabicyclo[2.2.1]hept-5-en-1-yl derivatives can be converted with high stereoselectivity into polypropionate fragments such as (-)-(2R,3R,4R,5S)-5-(benzyloxy)-3-(isopropyloxy)-2,4-dimethylhept-6-enal ((-)-16) or (-)-(2R,2'S,3'S,4'S,5'S)-2-[4-(benzyloxy)tetrahydro-3,5-dimethyl-5-metho xyfur-2-yl]propanal ((-)-20). The latter underwent stereoselective cross-aldolization with the lithium enolate of (+)-(1S,4S,5S,6S)-6-exo-(benzyloxy)-1,5-endo-dimethyl-7-oxabicyclo[2.2.1 ]heptan-2-one ((+)-9) giving an aldol ((-)-23); like mode of aldolization) that can be converted into a polypropionate fragment containing nine contiguous stereogenic centers.

Official source

https://infoscience.epfl.ch/entities/publication/8dc38944-6204-43d5-a228-2dbb7ec2d685

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Pierre Vogel
1994
Journal Articles

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/8dc38944-6204-43d5-a228-2dbb7ec2d685

About this result

Related concepts (8)

Chiral auxiliary

In stereochemistry, a chiral auxiliary is a stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis. The chirality present in the auxiliary can bias the stereoselectivity of one or more subsequent reactions. The auxiliary can then be typically recovered for future use. Most biological molecules and pharmaceutical targets exist as one of two possible enantiomers; consequently, chemical syntheses of natural products and pharmaceutical agents are frequently designed to obtain the target in enantiomerically pure form.

Enolate

In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds. Enolate anions are electronically related to allyl anions. The anionic charge is delocalized over the oxygen and the two carbon sites. Thus they have the character of both an alkoxide and a carbanion. Although they are often drawn as being simple salts, in fact they adopt complicated structures often featuring aggregates.

Stereoselectivity

In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during a non-stereospecific creation of a new stereocenter or during a non-stereospecific transformation of a pre-existing one. The selectivity arises from differences in steric and electronic effects in the mechanistic pathways leading to the different products. Stereoselectivity can vary in degree but it can never be total since the activation energy difference between the two pathways is finite: both products are at least possible and merely differ in amount.