Suzuki Arylation of 1,1-Dibromo-1-alkenes: Synthesis of Tetra-substituted Alkenes
作者:Annette Bauer、Michael W. Miller、Susan F. Vice、Stuart W. McCombie
DOI:10.1055/s-2001-10776
日期:——
1,1-Dibromo-1-alkenes were coupled with a variety of aryl boronic acids using Suzuki conditions (PdCl2(PPh3)2/Na2CO3/THF-H2O or DME-H2O/65-90 °C). The 1,1-dibromo-1-alkenes were prepared from ketones, and thus, the overall process furnished tetra-substituted alkenes in a very efficient manner.
The Interaction of π Orbitals with a Carbocation over Three σ Bonds
作者:Joseph B. Lambert、Sol M. Ciro
DOI:10.1021/jo951643d
日期:1996.1.1
The semi-pi analogue of double hyperconjugation (''hyperconjugation/conjugation'') has been examined in 4-isopropylidenecyclohexyl mesylate (4-OMs) by comparison with the saturated analogue, trans-4-isopropylcyclohexyl mesylate(5-OMs). The unsaturated substrate reacts in 97% trifluoroethanol only four times faster than the saturated substrate. Raber-Harris plots indicate that both substrates react by k(s) mechanisms; i.e., solvolysis occurs with solvent assistance rather than carbocation formation. These results are consistent with the absence of a direct, through-bond interaction of the double bond with the reactive center. The absence is caused at least in part by less than ideal overlap of the gamma, delta pi orbitals with the alpha,beta sigma orbitals. In contrast, an electron-rich tin atom attached to the 4-position provides a large rate enhancement and changes the mechanism to carbocation formation through double hyperconjugation.