235093-95-5Relevant academic research and scientific papers
A novel case of diastereoselection in 5-exo radical cyclization promoted by hydrogen bonding
Pedrosa, Rafael,Andres, Celia,Duque-Soladana, Juan P.,Mendiguchia, Pilar
, p. 3727 - 3730 (2007/10/03)
Moderate stereocontrol in 5-exo radical cyclizations of N,N-disubstituted (-)-8-amino menthol derivatives, promoted by tributyltin hydride and AIBN, was achieved. The stereoselection was explained in terms of hydrogen bond formation in the 1,3-amino alcohol derivative. The presence of one additional stereocenter at the allylic chain enhanced the stereoselection giving a single cyclization stereoisomer. The cyclization products were easily converted into enantiopure 3-alkyl- or 2,3-dialkyl-substituted pyrrolidines.
Regio- and stereoselective 5-exo radical cyclizations on a chiral perhydro-1,3-benzoxazine moiety. An access to enantiopure 3-alkylpyrrolidines
Andres, Celia,Duque-Soladana, Juan P.,Pedrosa, Rafael
, p. 4273 - 4281 (2007/10/03)
Both enantiomers of chiral, nonracemic 3-alkyl-substituted pyrolidines are prepared by diastereo-selective 5-exo-trig cyclization on (-)-8- aminomenthol-derived perhydro-1,3-benzoxazines used as chiral auxiliaries, followed by elimination of the menthol appendage. The diastereoselective radical cyclization is promoted by tributyltin hydride and occurs on a 3- aza-5-hexenyl-type radical, leading to five-membered rings in high yield. The stereocontrol of the cyclization is strongly influenced by 1,3-allylic strain so that an appropriate substitution pattern on the olefin-acceptor and the presence of a vicinal stereocenter are crucial for achieving good diastereoselectivity. The enantiopure pyrrolidines are obtained in three steps with concomitant recovering of the starting (+)-pulegone auxiliary.
