Reactions of 1-tosyl-3-substituted indoles with conjugated dienes under thermal and/or high-pressure conditions

The behavior of 1-tosyl-3-acetylindole (1a), N,N-diethyl-1-tosyl-3-indolegl yoxylamide (1b), and 1-tosyl-3-nitroindole (1c) as dienophiles in Diels-Ald er reactions under thermal and/or high-pressure conditions was explored wit h different dienes: isoprene (2), 1-(N-acetyl-N-propylamino)-1,3-butadiene (3), and 1-methoxy-3-trimethyisilyloxy-1,3-butadiene (Danishefsky's diene) (4). Compared to the acylated indoles, the nitro derivative proved to be th e best dienophile. In general, the use of Danishefsky's diene led to high-y ielding reactions under milder conditions. Likewise, high-pressure conditio ns proved to be better in producing high yields of products. The advantage of high-pressure over thermal conditions was the ability of the former to g enerate highly functionalized adducts in better yields, which were otherwis e very difficult or impossible to obtain. The use of thermal or high-pressu re conditions led to different regio- and/or stereoselectivity in the adduc ts, allowing control of the regio- or stereoisomer produced.