Regio- and Stereo-Selective Synthesis of Allylic Spiroethers (Spirobenzofuranes) via Intramolecular Mizoroki-Heck Reaction

Palladium(0)-catalyzed intramolecular annulation of twelve 1,3-disubstituted cyclopentenes, derived from (+)-vince lactam, resulted in 5-exo cyclizations, furnishing a series of 2,5-dimethyl-1-((3R,4'S)-2H-spiro[benzofuran-3,1'-cyclopentan]-2'-en-4'-yl)-1H-pyrroles in excellent diastereoselectivities and useful isolated yields. The double bond migration process, following the arylpalladium insertion, was controlled by fine-tuning of the reaction system, providing regioselectivities of up to 98:2. The selective Mizoroki-Heck reaction was used as the key transformation for preparing two new spirocyclic monoprotected amino acids as single diastereoisomers.