Phosphine-catalyzed [4+2] annulations of 2-alkylallenoates and olefins: synthesis of multisubstituted cyclohexenes.

ABSTRACT: From our investigations on phosphine-catalyzed [4+2] annulations between ?-alkyl allenoates and activated olefins for the synthesis of cyclohexenes, we discovered a hexamethylphosphorous triamide (HMPT)-catalyzed [4+2] reaction between ?-alkyl allenoates 1 and arylidene malonates or arylidene cyanoacetates 2 that provides highly functionalized cyclohexenes 3 and 4 in synthetically useful yields (30-89%), with moderate to exclusive regioselectivity, and reasonable diastereoselectivity. Interestingly, the [4+2] annulations between the ?-alkyl allenoates 1 and the olefins 2 manifested a polarity inversion of the 1,4-dipole synthon 1, depending on the structure of the olefin, thus providing cyclohexenes 3 exclusively when using arylidene cyanoacetates. The polarity inversion of ?-alkyl allenoates from a 1,4-dipole A to B under phosphine catalysis can be explained by an equilibrium between the phosphonium dienolate C and the phosphorous ylide D.

SUBMITTER: Tran YS 

PROVIDER: S-EPMC4122298 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature