NOVEL OXA-CAGE COMPOUNDS - SYNTHESIS, STRUCTURES, AND THE FORMATION MECHANISM OF TETRAACETAL OXA-CAGES AND CONVEX TETRAQUINANE OXA-CAGES

Abstract

Several novel tetraacetal era-cage compounds 5a-d and convex tetraquinane era-cage compounds 16a-d and 17b-d are synthesized from alkylfurans in three steps. Ozonolysis of the cis-endo-1,4-diones 3a-d in dichloromethane at -78 degrees C followed by reduction with dimethyl sulfide gives the era-cages 5a-d in high yields, respectively. The structures of these new tetraacetal era-cages are deduced from their spectral data and proven for the first time by X-ray analysis of the crystalline compound 5a. Ozonolysis of 3a-d in dichloromethane at -78 degrees C followed by treatment with triethylamine gives the convex tetraquinane era-cages 16a-d and 17b-d in 85-90% yields, respectively. The structures of these novel convex tetraquinane era-cages are finally proven by X-ray analysis of the crystalline compound 16a. Two reaction mechanisms via the common final ozonides are proposed for the formation of these two different types of era-cage compounds. The structures of the final ozonides formed by ozonolysis of the norbornene derivatives 3 are deduced to be 9 with endo stereochemistry on the basis of their spectral data and the formation of these two types of era-cages from the final ozonides. In reaction with the final ozonides, triethylamine is found to act as a base instead of a reducing agent, a different function from that of dimethyl sulfide. The synthesis of era-cages 24 and 25, which possess aromatic substituents directly on the skeleton, has also been accomplished.