A new protocol to obtain 3-substituted 2-cyclohexenones, was developed by reversing the chemical reactivity of 2-cyclohexenone. One-pot synthesis of 3-substituted 2-cyclohexenones can be achieved by treatment of 3-phenylthiosilyl enol ether with a mixture of t-BuLi/HMPA that allows hydrogen-selective exchange in presence of reactive electrophiles such as aldehydes, ketones and alkyl halides. This affords
The first totalsynthesis of an arcutine-type C20-diterpenoid alkaloid arcutinine has been achieved in both racemic and asymmetric forms. Construction of the C4 quaternary center and the pyrrolidine E ring in an early stage proved to be important for achieving the successful synthesis of the target alkaloid. Strategically, an asymmetric conjugate addition/aldol cascade and a decarboxylative allylation
Palladium-catalyzed cross-coupling reactions of arylmetal compounds with β-substituted α-iodoenones and a cyclohexyl triflate
作者:Folkert Boße、Ashok Rao Tunoori、AndréJ. Niestroj、Oliver Gronwald、Martin E. Maier
DOI:10.1016/0040-4020(96)00489-9
日期:1996.7
Electron-rich arylstannanes were found to couple with α-iodoenones in the presence of Pd2(dba)3·CHCl3, a weak-coordinating ligand [AsPh3 or Pd(o-tol)3] and CuI (0.75-1.0 equiv) to give sterically hindered α-arylcyclohexenones 15–20. In addition, compounds 19, 22 and 23 were prepared by Suzuki coupling reactions of the cyclohexyl derivatives 7c,f and 11, respectively, with the arylboronic acid 21.
Alpha-Halogenoalkyl carboxylates (FG-R1CH(X)(OCOR2); FG = COOR, CN, SR; X = I, Br) were readily prepared by the addition of an acid chloride or bromide (R2COX; X = Br or Cl) to an aldehyde (FG-RCHO) in the presence of a catalytic amount of ZnCl2. They insert efficiently zinc dust in THF-DMSO (X = Br, 8-10-degrees-C, 6-10 h) affording the corresponding zinc organometallics at the a position to oxygen FG-RCH(ZnBr)(OAc). After the addition of the THF-soluble copper salt CuCN.2LiCl, the corresponding copper reagents FG-RCH(Cu(CN)ZnBr)(OAc) are formed and reacted with various classes of electrophiles such as acid chlorides, aldehydes, enones, allylic and alkynyl halides, activated alkynes, nitro olefins and alkylidenemalonates providing polyfunctional molecules in excellent yields. Similarly, zinc organometallics at the a position to the nitrogen of cyclic imides were prepared by the zinc insertion to cyclic alpha-chloromethyl (or alpha-chloroethyl) imides. After their transmetalation to the corresponding copper organometallic ((R1CO)2NCH(R)(Cu(CN)ZnCl); R = Me or H), they were reacted with allylic and alkynyl halides and ethyl propiolate affording polyfunctional imides. The reaction of cyclic N-(chloromethyl)imides with aldehydes in the presence of chromium(II) chloride in THF furnishes protected amino alcohols in 36-95% yield.
Nucleophilic reactivity of zinc and copper carbenoids. Part II
作者:Paul Knochel、Tso Sheng Chou、Huai Gu Chen、Ming Chang P. Yeh、Michael J. Rozema