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Preparation of b-trialkylstannyl-a, b-unsaturated carbonyl compounds and their conversion to vinyllithium reagents

University of British Columbia

The preparation and synthetic utility of various β-trialkylstannyl-α,β-unsaturated carbonyl compounds is described. In this connection, treatment of tetrahydrofuran solutions of Me₃SnLi and n-Bu₃SnLi with one equivalent of PhSCu led to the in situ formation of PhS(Me-₃Sn)CuLi 72 and PhS (n-Bu₃Sn)CuLi 73, respectively. The latter reagents readily transferred, in a conjugate sense, the trialkyl-stannyl group to α,β-unsaturated carbonyl systems. In particular, these trialkylstannylcuprate reagents efficiently transformed β-iodo enones 4 into β-trialkylstannyl-α, β-unsaturated ketones 11, a new class of organotin derivatives. Likewise, treatment of the β-iodo enones 4_with Me₃SnCu • LiBr • SMe₂ 94, prepared by the reaction of Me₃SnLi with one equivalent of Me₂S*CuBr, gave the corresponding 6-trimethylstannyl enones in good yield. Two of these β-trialkylstannyl enones, β-trimetehyl-stannyl-2-cyclohexen-l-one 70 and β-tri-n-butylstannyl-2-cyclohexen-l-one, 74 were transformed into the vinylithium reagent 111. Sequential treatment of the enones 70 and 74 with lithium diisopropylamide and tert-butyldimethylsilyl chloride in the presence of hexamethylphosphoramide gave the enol silyl ethers 110 and 108, respectively. Transmetalation of the compounds 110 and 108 was accomplished by treatment of these substances with 1.1 equivalent of an alkyllithium reagent. Reaction of the resultant vinyllithium reagent 111 with electrophilic reagents proceeded smoothly to afford the corresponding substituted 1,3-cyclohexadienes in good yield. The reaction of PhS(Me₃Sn)CuLi 72 with various a, 6-acetylenic esters is also described. The course of the reaction could be controlled experimentally so as to produce, highly stereoselectively, either the (E) - or the (Z)-β-trimethylstannyl-α, β-unsaturated esters. Treatment (THF, -78°C) of PhS (Me₃Sn)CuLi 72 with a, β-acetylenic esters in the presence of a proton source (e.g., MeOH) gave the corresponding (E)-S-trimethylstannyl-a,g-unsaturated esters in good yield. Reaction of 7_2 with α,β-acetylenic esters at slightly higher temperatures (-48°C) in the absence of a proton source resulted in the formation of the corresponding (Z)-isomers. Reaction of ethyl (Z)-3 -tosyloxyacrylate 180 with Me₃SnCu*LiBr-SMe₂ 94 and n-Bu₃SnCu•LiBr*SMe₂ 181 gave the corresponding (Z)-β-trialkylstannylacrylates. Finally, two of the β-trimethylstannyl esters, ethyl (E)-3-trimethy1stanny1-2-butenoate 163 and ethyl (Z)-3-trimethylstannyl-2-butenoate 166, were converted into the geometrically isomeric trimethylstannyl dienes 184 and 185, respectively. Both of these substances underwent rapid and complete transmetalation when treated with 1.2 equivalents of methyllithium in tetrahydrofuran. The resultant 4-lithio-l,3-pentadienes (186 , 187) reacted smoothly with a variety of electrophiles to produce the corresponding substituted dienes (192 and 193).

Text

2010-03-30

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http://hdl.handle.net/2429/23152

Chemistry

University of British Columbia

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