Palladium(0)-Catalyzed 'Anti-Wacker'-Type Alkylative Cyclization of Alkynals

摘要

Transition metal-catalyzed, cis-addition specific coupling reactions between alkynes. carbonyls and organometallic reagents serve as a powerful one step methods to prepare synthetically useful allylic alcohols. Particularly interesting are intramolecular versions of this process using less nucleophilic organometallics 5 containing B. Zn. and Zr. which transforms simple precursors 1 into complex, cyclic allylic alcohols 2 that contain exo-tetra-substituted olefin groups (Scheme 1). Despite their desirability in terms of diversity-oriented synthesis, catalysts that promote the corresponding trans addition process leading to geometrically related cyclic allylic alcohols 4 or cycloalkenols 3 have not been reported. Below, we describe newly discovered palladium/monophosphine catalyzed trans-selective alkylative cyclization reactions of alkynals 1 with organoboronic reagents 6. in which alkyne substituents and phosphine ligands govern the ratios of the endo- and exo-cyclic allylic alcohol products (3 and 4).