Stereoselectivity of the captodative alkenes 1-acetylvinyl arenecarboxylates in Diels-Alder reactions with cyclic dienes and stereospecific rearrangement of their bicyclo[2.2.n] α-ketol adducts

Captodative alkene 1-acetylvinyl p-nitrobenzenecarboxylate 1a was evaluated for its reactivity and stereoselectivity with cyclohexadiene (10) in Diels-Alder reactions, showing exclusive endo preference. The two hydrolyzed products of the endo and the exo adducts obtained from the Diels-Alder cycloaddition between 1a and cyclopentadiene (7) were 8b and 9b. When treated with mCPBA, a ring expansion took place to stereospecifically yield the novel 3-oxatricyclo[3.3.1.0^2,4]nonanone acyloins 15 and 16, respectively. In the case of the α-ketol bicyclo[2.2.2]octanes 11b and 12b, the epoxidation/Baeyer-Villiger cascade process was preferred, resulting in the syn ketoepoxide 19b from each isomer. A synthetic application of this kind of transformation was carried out by reacting ketols 8b and 9b with an excess of mCPBA through a five-step cascade process to yield the bicyclic lactone 27 as a potential precursor of racemic β-carbaxylose.