An Improvement of the Preparation of Methyl-Substituted 5-Germaspiro[4.4]nonadienes: First Synthesis of 5-Germaspiro[4.4]nona-2,7-diene

Abstract

5-Germaspiro[4.4]nona-2,7-dienes partially or entirely methyl-substituted on the double bonds have been prepared recently in a low yield (8–32%) by cyclization of a dihalogermacyclopentene with lithium in the presence of a conjugated diene. We found that the reaction of diethoxygermanium dichloride or ethoxy(chloro)germacyclopent-3-enes with isoprene or 2,3-dimethylbutadiene and active magnesium gives the same germaspirodienes in yields about twice as great as by the previous method. The reaction of cyclization also occurs with butadiene, allowing isolation of the new unsubstituted 5-germaspiro[4.4]nona-2,7-diene.