1,3:2,4-di- O-benzylidene- l-arabinitol and observations on some related cyclic phenylboronates

Abstract

Benzylidenation of l-arabinitol using zinc chloride or sulphuric acid affords mainly 1,3- O-benzylidene- l-arabinitol, and a small amount (<5%) of 1,3:2,4-di- O-benzylidene- l-arabinitol, the structure of which has been established. The conformation of the dibenzylidene derivative is considered on the basis of n.m.r. spectroscopic data. As expected, 1,3- O-benzylidene- l-arabinitol affords the 4,5- O-isopropylidene derivative, but condensation with phenylboronic acid involves the 2,4-positions. 3,4- O-Isopropylidene- l-rhamnitol gives a 1,2-phenylboronate. The phenylboronate group was readily removed from each of the above esters to yield the unchanged parent compound, thus further exemplifying the use of this group as a blocking agent in carbohydrate chemistry.