Polylithiation of thioethers: a versatile route for polyanionic synthons

摘要

The successive reaction of phenyl vinyl thioether (1) wiht n-butyllithium and electrophile [E_1=PhCHO,(CH_2)_4CO,(CH_2)_5,CO] in THF at -78degC gives,after hydrolysis,the expected methylenic hydroxyl thioethers (2).Deprotonation of 2 with n-butyllithium followed by a DTBB-catalysed lithiation and reaction with a second electrophile [E_2=~tBuCHO,PhCHO,Me_2CO,(CH_2)_5CO],at -78degC, gives after hydrolysis the corresponding methylenic diols 3.The same diols can be prepared starting from 1 in a one-pot process without isolation of the hydroxy thioether 2.The sam emethodology was applied to teh cyclopropyl phenyl thioether (4),cyclopropyl 1,3-diols 5 {E_1=~tBuCHO,PhCHO,[Me_2(CH_2)_4]_2CO,(CH_2)_7CO; E_1=~tBuCHO,Me_2CO,(CH_2)_5CO} being isolated in moderate yieds.The successive treatment fo bis(phenylthio)methane (7) wiht : (a) n-butyllithium at 0degC,(b) a carbonyl compound [E_1=~tBuCHO,Me_2CO,Et_2CO,(CH_2)_5CO],at -40degC, (c) lithium and catalytic amount of DTBB (5%) and (d) a second carbonyl compound [E_2=~tPrCHO,~tBuCHO,PhCHO,Me_2CO,Et_2CO,(CH_2)_5CO] both at -78degC leads,after hydrolysis,to the expected dihydroxy thioethers 8.When after step (d),a second DTBB-catalysed ithiation is performed at temperatures ranging between -78degC and 20degC,the corresponding allylic alcohols 9 were isolated.Finally,treatment of alcohols 9 wiht a few drops of 6 M hydrochloric acid gives dienes 10 in almost quantitative yields.