Studies On The New Synthesis Of Pyranoid Glycals And Its Derivatives

The thesis includes three parts:1.Study on the efficient synthesis of pyranoid glycals;2.High stereoselective synthesis of C-alkynyl glycosides with the metal-free catalyst;3.Study on the new synthesis of the Perlin aldehydes.1.As versatile and useful intermediates,glycals are widely used in the organic synthesis of O-glycosides,C-glycosides,S-glycosides,N-glycosides and natural products.They have also been used in the glycosylations as glycosyl donors or acceptors.In this section,a simple and environmentally benign procedure was designed for preparation of pyranoid glycals.In a novel fashion,a series of protected glycopyranosyl bromides undergo the reductive elimination in the presence of zinc and ammonia chloride in CH3CN at 30-60℃.A variety of protecting groups,including acetyl,benzoyl,methanesulfonyl,p-tolylsulfonyl and azido groups,were stable under the reaction conditions.The corresponding glycals were obtained with excellent isolated yields(72-96%)in a short time(20-50min).Besides,the same methodology was also shown to be reliable to multigram-scale amount of the starting acetobromoglucose substrates(20g,86%yield).2.Stereoselective synthesis of C-glycosides has become very significant in the fields of carbohydrate and biological chemistry,since C-glycosides widely exist in the biologically active natural products.C-glycosides,specifically C-alkynyl glycosides are versatile chiral building blocks for the synthesis of many biologically natural products In this section,a metal-free and high stereoselective procedure for the synthesis of 2,3-unsaturated-C-glycosides have been developed between glycals and unactivated aryl acetylenes in the presence of TMSOTf.A series of 2,3-unsaturated-C-glycosides(20 examples)were obtained in mediate to good yields(50-70%)at a short time(3-25min),and all the products were confirmed as a singleα-isomer without any anomerization.And a plausible mechanism for the synthesis of alkynyl C-glycosides was depicted.3.Glycal-derived δ-hydroxy-α，β-unsaturated sugar aldehydes,commonly known as Perlin aldehydes.Perlin aldehydes were widely used in the synthesis of a variety of natural products and biological important molecules,since they have contained two predefined chiral centers and a wealth of functional groups,such as hydroxyl group,aldehyde group and conjugated double bond.In this section,a convenient and rapid method for the synthesis of Perlin aldehydes was developed.A series of glycal derived δ-hydroxy-α,β-unsaturated aldehydes were obtained in mediate to very good yields(48-86%)at a short time(5-15min)using FeCl3·6H2O as catalyst in CH3CN/H2O(volume ratio 90/1)at 80 ℃.The reaction avoided using the high toxic mercuric salt,the noble metal catalyst and the high reaction temperature.