Reactions of germenes with various naphthoquinones controlled by substituent effects.

The germene Mes(2)Ge=CR(2) (Mes = 2,4,6-trimethylphenyl, CR(2) = fluorenylidene) reacts with 5-methoxy-1,4-naphthoquinone to yield, via the o-quinodimethane , the endoperoxyde by simple reaction with molecular oxygen. By contrast, with 2,3-dichloro-1,4-naphthoquinone gives the tetracyclic compound by a double [2 + 4] cycloaddition between the Ge=C double bond and the conjugated system O=C-CH=CH. The new steric demanding germene Mes(2)Ge=CR'(2) (CR'(2) = 2,7-di-tert-butylfluorenylidene) undergoes similar [2 + 4] cycloadditions with various substituted or unsubstituted naphthoquinones, leading to tetracyclic adducts . The germene , the endoperoxide and the cycloadducts and have been structurally characterized.