Enyne asymmetric 1,4-diene formation

Several groups exploited the power of the intermolecular Diels-Alder reaction early in their syntheses for the formation of substituted cyclohexenes. In his synthesis of platencin, Nicolaou used a Danishefsky-like diene in an asymmetric Diels-Alder reaction for the synthesis of a chiral cylohexenone. Kanai and Shibasaki developed a catalytic asymmetric Diels-Alder reaction promoted by barium isopropoxide for the first step in their synthesis of Tamiflu. Danishefsky constructed the cyclohexene ring in paecilomycine A by employing a highly e t/o-selective Diels-Alder reaction of siloxydiene 115 and enyne dienophile 116 to yield target 117. ... 

Inducing Asymmetry in -Elimination Pathway Apart from its racemic variants, cycloisomerization of enynes has been successfully employed in asymmetric synthesis. In the first example of an asymmetric cycloisomerization reaction, Trost et al. used a combination of palladium(O) and a chiral acid to catalyze the cycloisomerization of 1,6-enynes resulting in a rather low enantioselectivity of 33% ee for the formation of 1,4-diene (35) (Scheme 7.17(a)) [35]. Modem development of chiral phosphoric acids has allowed the reexamination of this approach. Thus, when palladium(O) and chiral (5)-TRIP were used with enyne 36 a 71% yield of diene 37 was isolated in 88% ee [36]. Under the same eon-cept, Mikami and coworkers found that cationic palladium... 

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