Cyclization dichotomy of D-xylo-hex-5-ulosonamides and synthesis of piperidine analogs of aldohexoses and aldohexono-1,5-lactones

The preparation of 2,3,4,6-tetra-O-benzyl-5-D-xylo-hex-5-ulosonamides 3a an d 3b and their cyclization to 5-amino-2,3,4,6-tetra-O-benzyl-5-deoxy-D-gluc ono-1,5-lactam (4) and 5-amino-2,3,4, 6-tetra-O-benzyl-5-deoxy-5-talono-1,5 -lactam (5) or to 2,3,4,6-tetra-O-benzyl-1,5-dideoxy-1,5-imino-D-glucitol ( 9), and also their direct transformation into 2,3,4,6-tetra-O-benzylo-D-tal ono-1,5-lactone (6), are described and discussed. The atypical boat conform ation of D-talonolactam 5 and D-talonolactone 6 was found.