METALLOLES-14 CHEMISTRY

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Abstract
In order to obtain β-functionalized 1-sila (or germa)-cyclopent-2-enes (M = Si, Ge; R1, R2 = Me or Ph; R3, R4 = H or Me) (I) various oxidation methods of metallacyclopent-3-enes have been examinated. The resulting metallacyclopent-4-ene-3-ols (I, X = OH) were converted into phenylcarbamates (I = OC(O)NHPh) or S-methylxanthates (I = OC(S)SMe) and their utility as intermediates in the synthesis of metalloles (siloles and germoles) was investigated. Depending on the experimental conditions, catalytic dehydration of metallacyclopentenols or thermolysis of carbamates or xanthates give various dienes via four different reaction processes: i) β-elimination C-M; ii) β-elimination C-H; iii) isomerization of C-methylated metalloles; iv) catalytic demetallation. The thermolysis of arylcarbamates is the best method for conversion of I to metalloles, specially for the synthesis of remarkably dimerization-stable 1,1-R1R2-3,4-dimethylmetalloles (≥ 80% yield). A one pot synthesis of these stable metalloles from the corresponding alcohol and phenyl isocyanate is proposed. Unstable monomeric metalloles are stabilized by transition metal complexes or trapped by a (4 + 2) cycloaddition.