ADDITION OF CYCLOPENTADIENE AND 2-TRIMETHYLSILYLOXYFURAN TO QUINONES BEARING A MENTHYL ESTER CHIRAL AUXILIARY

Addition of cyclopentadiene to 2-carbomethoxy-1,4-benzoquinone 9 affor ded Diels-Alder adduct 10 using the Lewis acids ZnCl2 and ZnBr2 wherea s the fragmenatation product 11 was the major product when using SnCl4 and TiCl4. Addition of cyclopentadiene to 1,4-benzoquinone 8 bearing a menthyl ester at C-2 afforded Diels-alder adduct 12 in moderate dias tereomeric excess using ZnCl2 and ZnBr2 as Lewis acids. Use of TiCl4 a nd SnCl4 afforded the fragmentation product 13 also in moderate diaste reomeric excess. Addition of 2-trimethylsilyloxyfuran to chiral naphth oquinone 4 and benzoquinone 8 afforded furofuran adducts 14 and 15 res pectively as a 1:1 mixture of diastereomers. (C) 1998 Elsevier Science Ltd. All rights reserved.