Synthesis of Hindered and Functionalized 1-CF3 Substituted Olefins via a Carbolithiation−Elimination−Metalation Cascade
摘要:
Addition of organolithium reagents to trifluoromethyl enol ethers 1a-d and thio enol ethers 2a provided stereoselectively the corresponding trisubstituted fluoroalkenes 3a-d in 70-90% yields. The products could themselves react with organolithium reagents and undergo a vinyl metalation providing, after trapping with an electrophile, tetrasubstituted olefins in excellent yields and with stereoselectivity. This method can be applied to other fluoroalkyl enol ethers (Rf = C2F5). The product, tetrasubstituted olefin, can be obtained directly from enol ether with 2 equiv of reagent through a carbolithiation-elimination-metalation cascade.
A concise preparation of tetrasubstituted hindered functionalized CF3-olefins 2-7 from corresponding enol ether 3 is described. Geometrically pure gamma-CF3,gamma-alkyl allylic alcohol thus prepared could undergo Claisen-type rearrangements and provide, in good yields, carboxylic esters and amides containing a beta- quaternary CF3-substituted carbon.