Journal of the American Chemical Society, Vol.131, No.15, 5382-5382, 2009
Directed Carbozincation Reactions of Cyclopropene Derivatives
A diastereoselective procedure has been developed for the Cu-catalyzed addition of diorganozinc reagents to cyclopropene derivatives. Ester and oxazolidinone functions direct the addition of a variety of organozinc reagents with excellent facial selectivity. The resulting cyclopropylzinc reagents can be captured via stereospecific reactions with electrophiles. Cycloprop-2-ene carboxylic esters, which are directly available from the transition-metal-catalyzed reactions of alkynes with alpha-diazo esters, can be utilized directly in carbozincation protocols. Both diastereoselectivity and regioselectivity are high for the carbozincation reactions of 2-alkylcycloprop-2-ene carboxylate esters. The scope of the method is broadened by the ability to utilize organozinc: reagents that have been generated in situ from Grignard reagents. Chiral oxazolidinone auxilaries are effective in controlling the diastereoselectivity of the carbometalation reactions.