Abstract
The studies on the Diels-Alder reaction of masked o-benzoquinones (MOBs) 75 with racemic and chiral furans and the synthesis of chiral tricyclic g-lactones 93a-c,e-g are described.The Diels-Alder reactions of several masked o-benzoquinones (MOBs) 75 with racemic furans 78-80 were investigated. When the R-group of 78-80 is isopropyl, the resultant cycloadducts (+)-84a-c,e-g, were obtained in good yields and in excellent diastereoselectivites (~90-98% d.e.). The Diels-Alder reactions of MOBs 75 with chiral furans (+)-78, 80, 81 proceeded in the similar way to furnish the cycloadducts (+)-87a-c,e-g in good yields with excellent diastereomeric excess (~92-99% d.e.). The assigned absolute configurations of (+)-87a-c,e-g were based on single crystal X-ray analysis and CD spectra.The Diels-Alder adducts (+)-87a-c,e-g when subjected to hydrolysis under acidic conditions, and NaIO4 mediated oxidation provided the corresponding tricyclic g-lactones (+)-93a-c,e-g in high enantiomeric selectivities and high yields.