Synthesis of glycal-derived heterocyclic systems and their application in stereoselective glycosylation reactions. Methanolysis of O-functionalized epoxides and aziridines in the gas-phase

Allyl oxiranes derived from D-galactal and D-allal were synthesized and their addition reactions with O-, C-, S-, and N-nucleophiles were examined. A 1,4-regio- and á- or â-stereoselective or an 1,2-adddition pathway is commonly observed depending on the ability of the nucleophile to coordinate with the oxirane oxygen. The same study was led to allyl epoxides derived from 6-deoxy-D-galactal and 6-deoxy-D-allal in order to clarify if there was a synergic coordinating effect of the side chain O-functionality (-CH2OBn). N-mesyl and N-nosyl allyl aziridines derived from D-galactal and D-allal were synthesized and their addition reactions with O-, C-, S-, and N-nucleophiles (for N-mesyl aziridines) and with O-nucleophiles (for N-nosyl aziridines) were studied: as the consequence of the conjugate addition involved in this glycosylation process a N-mesylamino group (from N-mesyl aziridines) or a free amino group (from N-nosyl aziridines) was regioselectively delivered to the C(4) of the newly formed pseudoglycal system. A further interesting structural modification of these glycal systems was investigated: the substitution of the endocyclic oxygen with a N-substituted nitrogen that is the transformation of a glycal system into an imnoglycal system. Thus, iminoglycal-derived allyl oxiranes derived from D-galactal and D-allal were synthesized and their regio- and stereochemical behavior was examined in the addition reactions with O-nucleophiles. The regiochemical behavior of a series of aliphatic open chain epoxides and aziridines bearing a heterofunctionality in an allylic or homoallilyc relationship is examined in the opening reaction with MeOH under both condensed and gas phase operatine conditions. The results indicate that the proton (actually D+) possesses in the gas phase intrinsic chelating properties which are even superior than those of Li+ in the condensed phase. Allyl oxiranes derived from D-galactal and D-allal were synthesized and their addition reactions with O-, C-, S-, and N-nucleophiles were examined. A 1,4-regio- and á- or â-stereoselective or an 1,2-adddition pathway is commonly observed depending on the ability of the nucleophile to coordinate with the oxirane oxygen. The same study was led to allyl epoxides derived from 6-deoxy-D-galactal and 6-deoxy-D-allal in order to clarify if there was a synergic coordinating effect of the side chain O-functionality (-CH2OBn). N-mesyl and N-nosyl allyl aziridines derived from D-galactal and D-allal were synthesized and their addition reactions with O-, C-, S-, and N-nucleophiles (for N-mesyl aziridines) and with O-nucleophiles (for N-nosyl aziridines) were studied: as the consequence of the conjugate addition involved in this glycosylation process a N-mesylamino group (from N-mesyl aziridines) or a free amino group (from N-nosyl aziridines) was regioselectively delivered to the C(4) of the newly formed pseudoglycal system. A further interesting structural modification of these glycal systems was investigated: the substitution of the endocyclic oxygen with a N-substituted nitrogen that is the transformation of a glycal system into an imnoglycal system. Thus, iminoglycal-derived allyl oxiranes derived from D-galactal and D-allal were synthesized and their regio- and stereochemical behavior was examined in the addition reactions with O-nucleophiles. The regiochemical behavior of a series of aliphatic open chain epoxides and aziridines bearing a heterofunctionality in an allylic or homoallilyc relationship is examined in the opening reaction with MeOH under both condensed and gas phase operatine conditions. The results indicate that the proton (actually D+) possesses in the gas phase intrinsic chelating properties which are even superior than those of Li+ in the condensed phase.