求 核 剤 に よ る ス ピ ロ シ ク ロ プ ロ パ ン の- 開 裂 環 化 反 応 の 開 発 と そ の 応 用

Cyclopropanes serve as valuable building blocks in organic synthesis because of their high reactivity based on their strong ring strain. On the other hand, spirocyclopropanes have rarely been utilized in synthetic organic chemistry despite their high potential because of their low availability. Since we reported an efficient preparation method of cyclohexane-1,3-dione-2-spirocyclopropane and its ring-opening cyclization with amine to form a bicyclic compound, tetrahydroindol-4 (5H) -one, we have investigated reactions of spirocyclopropanes with various nucleophiles to provide the bicyclic heterocycles. In this account, we have summarized our research on the development of the reactions using unique nucleophiles possessing a leaving group moiety. Ring-opening cyclization of spirocyclopropanes with a catalytic amount of iodide, which acts as both a nucleophile and a leaving group, regioselectively produced 2- or 3-substituted tetrahydrobenzofuran-4-ones in high yields. In addition, stabilized sulfonium ylides and sulfoxonium ylides were used for the ring-opening cyclization of spirocyclopropanes and constructed chromane skeletons. We also show the utility of the ring-opening cyclization products, tetrahydroindol-4 (5H) -ones, as key intermediates for synthesis of highly substituted indoles and Aspidosperma alkaloids. Moreover, we demonstrated the synthesis of 1-azaazulenes employing ring-opening cyclization of cycloheptane-1,3-dione-2-spirocyclopropane with 2,4-dimethoxybenzylamine.