SYNTHESIS OF 3-SILYLATED AND 3-GERMYLATED 1-SILACYCLOPENT-3-ENE AND 1-GERMACYCLOPENT-3-ENE

The synthesis of allylic sila (and germa) cyclopentenes containing an Et(3)M (M = Si, Ge) group in vinylic position is described. 1-Germacyc lopent-3-enes 3-silylated (IIIa) and 3-germylated (IIIb) result from 1 ,4-cycloaddition of GeI2 to the corresponding 2-metallated 1,3-dienes (II). 3-Metallated 1-silacyclopent-3-enes (IIIc-IIlf) are obtained by two methods. One involves the reaction of dienes II with Me(2)SiCl(2), and Mg, leading to compounds IIIc (M = Si) and IIId (M = Ge). The oth er method corresponds to the trichlorosilylation (HSiCl3, Et(3)N, epsi lon Cu2Cl2) of dichlorinated compounds I resulting from cis-addition o f Et(3)MH to cis-1,4-dichlorobutyne. From the two trichlorosilylated d erivatives IV and V, formed in S(N)2 and S(N)2' reactions, only the 1- trichlorosilyl 2-triethylsilyl (and germyl) 4-chlorobut-2-enes (IV) gi ve, in the presence of magnesium, the 1,1-dichloro 3-triethylsilyl (an d germyl) 1-silacyclopent-3-enes (IIIe and IIIf).