Insertion of 1-Chloro-1-lithioalkenes into Organozirconocenes. A Versatile Synthesis of Stereodefined Unsaturated Systems

Abstract

Hydrozirconation of alkenes and alkynes, followed by insertion of 1-halo-1-lithio-1-alkenes, generated in situ by lithium tetramethylpiperidide deprotonation of vinyl halides, affords vinylzirconocene species which may be further elaborated. The method provides easy access to many structures including terminal (3 E )- and (3 Z )-1,3-dienes and (3 E,5 E )- and (3 Z,5 E )-1,3,5-trienes, and internal ( E, Z )-dienes, ( E, Z, E )-trienes, and (1 E,3 Z )-1,3-dien-5-ynes. Insertion of 2-monosubstituted 1-halo-1-lithio-1-alkenes occurs with clean inversion of configuration of the sp 2 -carbenoid carbon. Carbenoids derived by deprotonation of 2,2-disubstituted 1-halo-1-alkenes gave poor stereocontrol probably due to isomerization before insertion into the organozirconium species. Insertion of vinyl carbenoids into alkynylzirconocenes affords terminal (3 E )- or (3 Z )-1,3-dien-5-ynes, internal (1 E,3 Z )-1,3-dien-5-ynes, and ( Z )-3-en-1,5-diynes.