Synthesis of Dioxa-cage Compounds as a New Probe for the Stereochemistry of the Bisadducts of p-Benzoquinone with 1,3-Cyclodienes

摘要

π-Facial stereoselectivety in Diels-alder reactions and their synthetic applications have attracted considerable attention in recent years. In the Diels-Alder reaction of the cyclopentadiene-quinone cycloadduct 1 with cycloalkadiene, four bisadducts with different stereochemistry could potentially result endo-anti-endo 2, endo-antiexo 3, endo-syn-exo 4, and endo-syn-endo 5. Nevertheless, 2 was the only one formed directly in the cycloaddition of 1 with cyclodienes. The π-facial selectivity in Diels-Alderr reactions of compounds 6 and 7 with cyclodienes was reported and the stereochemistry of the cycloadducts was determined by exhausted chemical correlation, spectral comparsion, and x-ray analyses. We report here the synthesis of dioxa-cge compounds 8-11 as a new probe for the determination of the stereochemistry of the bisadducts of p-benzoquinone with cyclodienes. The synthesis of dioxa-cage compounds 8-11 from the bisadducts 2-5 was achieved by a very short sequence. The stereochemistry of the dioxa-cage 8-11 was unambiguously determined by H-H COSY and NOE experiments.