KETALS OF L-RHAMNOHEPTONOLACTONES - POTENTIAL MIMICS OF L-RHAMNOSE

Isopropylidene and cyclohexylidene ketals of gamma- and delta-heptonolactones derived from Kiliani ascensions of protected L-rhamnose may constitute suitable intermediates for the preparation of mimics of L-rhamnose. The X-ray crystal structure of 7-deoxy-3,4-O-isopropylidene-1-glycero-1-galacto-hepta 1,5-lactone provides an example of a delta-lactone in a boat conformation with a substituent in a flagpole position. The size of ring in the lactones is completely consistent with Hudson's classical lactone rotation rule of 1910.