Organocatalytic asymmetric synthesis of 5-(trialkylsilyl)cyclohex-2-enones and the transformation into useful building blocks.

A simple organocatalytic approach to highly attractive chiral building blocks is presented. By the reaction of beta-ketoesters with alpha,beta-unsaturated aldehydes using a chiral TMS-protected prolinol as the catalyst, optically active 5-(trialkylsilyl)cyclohex-2-enones are formed in good yields and with 98-99% ee. The applications of 5-(trialkylsilyl)cyclohex-2-enones for the formation of 5-(hydroxy)cyclohex-2-enones and the A-ring of 19- nor-1alpha,25-dihydroxyvitamin D3 are also presented.