Addition of cyclopentadiene and 2-trimethylsilyloxyfuran to quinones bearing a menthyl ester chiral auxiliary

Article abstract of DOI:10.1016/S0040-4020(98)00211-7

Addition of cyclopentadiene to 2-carbomethoxy-1,4-benzoquinone 9 afforded Diels-Alder adduct 10 using the Lewis acids ZnCl₂ and ZnBr₂ whereas 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 diastereomeric excess using ZnCl₂ and ZnBr₂ as Lewis acids. Use of TiCl₄ and SnCl₄ afforded the fragmentation product 13 also in moderate diastereomeric excess. Addition of 2-trimethylsilyloxyfuran to chiral naphthoquinone 4 and benzoquinone 8 afforded furofuran adducts 14 and 15 respectively as a 1:1 mixture of diastereomers.