title: A Practical Solution to Stereodefined Tetrasubstituted Olefins.
abstract: Olefins, compounds with a carbon-carbon double bond, are of fundamental importance, and stereodefined construction of tetrasubstituted carbon-carbon double bond is a significant challenge. Here we show a unique and practical method for the preparation of stereodefined, fully substituted olefins via conjugate addition of organozinc reagents to readily available 2,3-allenals. Through mechanistic studies, it is confirmed that the geometry of the newly formed double bond is controlled by unique regiospecific oxygen-protonation of the enolate intermediates, generating 1,3-alkadienols. Such alkadienols would undergo a concerted 1,5-H-transfer reaction via a six-membered transition state to ensure the configuration of the carbon-carbon double bond in the final products. Using the readily available organozinc reagents and 2,3-allenals provides a very rapid access to a wide range of tetrasubstituted olefins with defined stereochemistry, bearing an extremely versatile aldehyde functionality.
authors: Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University , Hangzhou 310027, Zhejiang, People's Republic of China.
authors: Jianxin
authors: J
authors: Dai
authors: Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University , Hangzhou 310027, Zhejiang, People's Republic of China.
authors: Minyan
authors: M
authors: Wang
authors: Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University , Hangzhou 310027, Zhejiang, People's Republic of China.
authors: Guobi
authors: G
authors: Chai
authors: Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University , Hangzhou 310027, Zhejiang, People's Republic of China.
authors: Chunling
authors: C
authors: Fu
authors: Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University , Hangzhou 310027, Zhejiang, People's Republic of China.
authors: Shengming
authors: S
authors: Ma