N-Substituted Oxazolidinones in the Preparation of Functionalized Chiral Auxiliaries Using Wittig Reagents
Mentor:David Marten, Professor of Chemistry, Westmont College
Wittig reagents are used in a reaction with aldehydes or ketones to form carbon-carbon double bonds. Wittig reagents containing chiral auxiliaries may be used to prepare alkenes that are then transformed in stereoselective ways using organometallic reagents to produce useful, chiral, organic compounds. Three chiral N-substituted oxazolidinones were used, in a previously unreported reaction, to produce Wittig reagents with an ester linkage to a chiral auxiliary containing an amide group. The use of an N-mesitoyl group with an (S)-5,5-dimethyl-4-phenyl substituted oxazolidinone resulted in a 91:9 E/Z ratio in the chiral enoate produced from the Wittig reaction with methylenetriphenylphosphorane [CH2=PPh3] followed by treatment with benzaldehyde. When an N-tosyl group was used with an oxazolidinone without the methyls, the Wittig reaction occurred as expected to yield a chiral enoate with a 95:5 E/Z ratio. Using the N-mesitoyl (S)-4-phenyl-oxazolidinone, the Wittig olefination occurred with 99% E selectivity. The preparation of these chiral intermediates will be described with a discussion of the stereoselectivity we are expecting to see in the reaction of the intermediates with organocopper-type reagents.