A comprehensive survey of Stille-type C-sp2-C-sp2 single bond forming processes in the synthesis of retinoic acid and analogs

The synthesis of the retinoid skeleton has been exhaustively explored using the Stille coupling for the formation of the side-chain single bonds. On e mploying the experimental catalytic conditions developed by Farina [Pd-2(db a)(3), AsPh3, NMP] we have modified the electronic and steric requirement o f the coupling partners, alkenyl stannanes and electrophiles (alkenyl iodid es and triflates). The comprehensive survey afforded appropriately matched components for every bond formation considered. Moreover, from the comparis on of the reactivities of different coupling partners with different degree s of steric hindrance, the sensitivity of the Stille coupling to steric eff ects was confirmed. Besides providing a variety of building blocks for reti noid synthesis, the study highlights some vends that might be useful for th e application of the Stille reaction to the synthesis of unsubstituted conj ugated polyenes. (C) 1999 Elsevier Science Ltd. All rights reserved.