Peterson alkenation stereocontrolled synthesis

Van Vranken and coworkers have illustrated an elegant use of convergent stereocontrol in Peterson olefinations. In their synthesis of ( )-3-hydroxybakuchiol, the reaction between a neopentyl a-silyl alkyllithium intermediate and an aryl aldehyde generated a mixture of syn- and anti-P-si y alkoxides. The mixture was treated under basic, kinetic conditions to give stereoselective elimination of the iyw-yS-silyl alkoxide thus affording an E alkene 93. Subsequent heating of the reaction mixture and addition of acid caused stereospecific elimination of the a r/-y9-silyl alkoxide resulting in the same E alkene via the complementary cationic pathway (see section 2.10.3). Excellent selectivity was obtained. 

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