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The addition of preformed ketone and ester enolates to a,bunsaturated aldehydes 1 followed by in situ protection leads to the carbonates 3, 7, 8, 11, and 13. They are converted into sensitive functionalized dienes 4, 9, 12, and 14 by a smooth palladiumcatalyzed elimination. Both syn-and anti-carbonates 7 and 8 lead to E-dienes 9 in a stereoconvergent manner.

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Syn-and anti-configured carbonates 6 a and 6 b, available from stereoselective aldol additions and subsequent protection with methyl chloroformate, serve as probes for the elucidation of the stereochemistry of the b-PdÀH elimination. Upon treatment with [Pd(PPh 3 ) 4 ], the carbonates 6 a and 6 b give the dienes 7 a and 7 b in different ratios; the latter stereoisomer 7 b is formed as a result of p ± s ± p conversions. Both syn and anti eliminations are shown to occur as competing reactions, the former one being the strongly preferred pathway. The highly reactive [Pd{P(nBu) 3 } 4 ] catalyst, generated in situ from Pd(OAc) 2 and P(nBu) 3 causes thermodynamic control in the elimination; thus, it serves as a smooth reagent for Z ± E isomerization.