Asymmetric 1,3-dipolar cycloadditions, diels-alder reactions, and allylations using new chiral auxiliaries

Abstract

The new chiral auxiliaries for the asymmetric reactions were synthesized from (S)-indoline-2-carboxylic acid. These derivatives provided high levels of asymmetric induction in 1,3-dipolar cycloadditions, Diels-Alder reactions, and allylations. New chiral acrylamides were prepared and examined in 1,3-dipolar cycloaddition of nitrile oxides. Nitrile oxide cycloaddition to dipolarophiles gave $\triangle^2$-isoxazolines with high diastereoselectivity (95:5). Asymmetric Diels-Alder reactions of the new chiral dienophiles with cyclopentadiene proceeded with excellent diastereomeric excesses (up to $>99\%$ de). In the case of (S)-N-Acryloylindoline derivatives (6a and 6c-d), inverse configuration were obtained depending on the Lewis acids. The structures of the Lewis acid-dienophile complex directed stereocontrolled asymmetric synthesis of the dramatically opposite enantiomers probably due to interactions between Lewis acids and the functional groups (hydroxy, ester and ether) of indoline derivatives. High diastereofacial selectivity could be achieved even in the noncatalyzed reaction with the dienophile 6b. Diastereoselective allylations of new chiral $\alpha$ - keto amides were examined by using allylating reagents (allylsilane and allylstannane) in the presence of various Lewis acids to give excellent diastereomeric excesses (up to 98\% de).