Structure and synthetic uses of cyclic benzeneboronates of polyhydroxy compounds

Abstract

1. Mass spectrometry has been employed to obtain information concerning the predominant structures of the cyclic benzeneboronates formed from two 1,6-dideoxy-hexitols and three 1-deoxy-pentitols. 2. The structures and relative abundances of the isomeric bisbenzene-boronates formed from each of seven pentitols have been elucidated through mass spectroscopic and methylation studies. The g.c.-m.s. analysis of the products obtained from methylation, partial hydrolysis and acetylation of the bisbenzeneboronates, showed that all of the pentitol boronates investigated contained more than one structural isomer. 3. The composition of the crude bisbenzeneboronate products have been rationalised from considerations of the possible conformations of the proposed structures. 4. The benzeneboronate of methyl 2-acetamido-2-deoxy-a-D-glucopyrano-side was synthesised in high yield. The structure was determined through mass spectrometric and methylation studies. 5. Using this aminoglycoside benzeneboronate, a derivative of a biologically important disaccharide was synthesised in excellent yield, illustrating the use of the cyclic benzeneboronate entity as a protective group. The configuration of the glycosidic linkage of the synthesised disaccharide was determined through infrared, proton magnetic resonance and polarimetric studies. 6. The selective replacement of a 2-plienyl-l,3,2-dioxaborolane ring by a 2,2-dimethyl-1,3-dioxolane ring with acidified acetone, termed ketoly-sis, was investigated. Methylation or trimethylsilylation or acetylation of the partially hydrolysed ketolysis product, followed by g.c.-m.s. analysis, afforded information concerning the structure of the monoketal produced. 7. The ketolysis reaction was applied to four polybenzeneboronateswhich contained five- and six-membered benzeneboronate rings. The results showed that a 2-phenyl-1,3,2-dioxaborolane ring can be selectively replaced by a 2,2-dimethyl-l,3-dioxalane ring in good yield. 8. The synthetic use of the selective ketolysis of benzeneboronateesters was demonstrated through the preparation of 1,2-0-isopropylidene-D-manhitol in good yield.