An Efficient Synthesis of Functionalized 1,6-Dienes from Baylis-Hillman Adducts via a Pd-Catalyzed Decarboxylative Protonation Protocol

摘要

Functionalized 1,6-dienes is a synthetically important skeleton and has been used for the synthesis of various carbocycles via a ring-closing metathesis (RCM) reaction and a Pd-cataly-zed cyclization/hydrosilylation. In addition, symmetric bis-cinnamic acid derivatives have been used for the synthesis of C2-symmetric core units of HIV protease inhibitors,spiro glutarimides and spiro bisglutarimides, and propellano bis-lactone derivatives. These functionalized 1,6-dienes are most commonly prepared by diallylation of active methylene compounds with allylic halides under basic conditions. Recently, a palladium-catalyzed allylation of active methylene compounds are using widely. Cinnamyl bromides, derived from the Baylis-Hillman adducts, has also been used in this way for the synthesis of symmetric bis-cinnamic acid derivatives. During our recent studies on Pd-catalyzed decarboxylative protonation, allylation, and elimination reactions with modified Baylis-Hillman adducts, we envisioned that synthetically interesting 1,6-diene derivatives 4 could be synthesized, as shown in Scheme 1.