A new route to chiral hydroxypyrrolidines from D-erythrose via intramolecular 1,3-cycloaddition

摘要: 2,3-O-Isopropylidene-D-erythrose (1) reacted with ethoxycarbonylmethylene(triphenyl)phosphorane in refluxing benzene to give the E and Z alkene esters (2a) (2b). The ester was converted, via 6-triflate (7a) 6-azide (3a), into dihydrotriazole (8) by 1,3-cycloaddition. Ring opening of compound sodium ethoxide gave pyrrolidine diazo (9) which on hydrogenolysis (2R,3S,4R)-ethyl (3,4-isopropylidenedioxypyrrolidin-2-yl)acetate (5). A similar series reactions from Z-ester (2b) (6), 2S-isomer Thermolysis (10), (9), gave(Z)-(3S,4R)-ethyl (3,4-isopropylidenedioxypyrrolidin-2-ylidene) acetate (12) reduced cyanoborohydride undergo rapid quantitative cyclisation presence ion. Kinetically β-isomer (18) is preferred [100% (2b), 86% (2a)]; at equilibrium α-isomer (19) favoured (82%).