Novel Oxa-Cage Compounds: Synthesis, Structures, and the Formation Mechanism of Tetraacetal Oxa-Cages and Convex Tetraquinane Oxa-Cages

Article abstract of DOI:10.1021/jo00128a031

Several novel tetraacetal oxa-cage compoundsa 5a-d and convex tetraquinane oxa-cage compounds 16a-d and 17b-d are synthesized from alkylfuranes in three steps.Ozonolysis of the cis-endo-1,4-diones 3a-d in dichloromethane at -78 deg C followed by reduction with dimethyl sulfide gives the oxa-cage 5a-d in high yields, respectively.The structures of these new tetraacetal oxa-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 deg C followed by treatment with triethylamine gives the convex tetraquinane oxa-cages 16a-d and 17b-d in 85-90percent yields, respectively.The structures of these novel convex tetraquinane oxa-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 oxa-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 oxa-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 oxa-cages 24 and 25, which possess aromatic substituents dirctly on the skeleton, has also been accomplished.