Azides, reaction with sulfonate esters

The importance of reactions with complex, metal hydrides in carbohydrate chemistry is well documented by a vast number of publications that deal mainly with reduction of carbonyl groups, N- and O-acyl functions, lactones, azides, and epoxides, as well as with reactions of sulfonic esters. With rare exceptions, lithium aluminum hydride and lithium, sodium, or potassium borohydride are the... 

A MW-assisted protocol for the synthesis of azides, thiocyanates, and sulfones has been developed (Scheme 12) that has proved to be a useful alternative, as the use of environmentally deterimental volatile chlorinated hydrocarbons is avoided.All the reactions with these readily available halides or tosylates have shown significant increase in reactivity, thus reducing the reaction times with substantial improvement in the yields. Various functional groups such as ester, carboxylic acid, carbonyl, and hydroxyl were unaffected under the mild reaction conditions employed. This method involves simple experimental procedures and product isolation which avoids the use of phase-transfer catalysts, and is expected to contribute to the development of greener strategy for the preparation of various azides, thiocyanates, sulfones, and other useful compounds. 

Azide is a potent nucleophile and can react with electrophilic substrates other than halides and sulfonate esters. Reaction of azide with the epoxide moiety in carboethoxy oxirane (ethyl glycidate) was followed by catalytic hydrogenation of the azide and hydrolysis of the ester to give isoserine (3-amino-2-hydroxypropanoic acid, 1.23). This synthetic approach to isoserine dates to 1879. 3... 

Nucleophilic Displacement. - Sulfonate ester displacement reactions continue to be widely applied in amino-sugar syntheses. The 3-amino-S-thioglucofuranose derivative 20 was obtained from the corresponding allofuranose 3-mesylate by displacement with azide ion and reducdon (liAlHJ (see also section 2.6)." The 2,3-epimino-a-D-lyxopyranoside 21 was prepared in 11 steps from diacetoneglucose via 3-azido-3-deoxy-1.2-O-isoprc ylidene-a-D-glucofriranose. Key steps were... 

Other systems that allow stereospecific substitution with retention include ester-activated chloride displacement by an amine (25 to 26) and sulfone-activated chloride displacement by azide (27 to 28). The choice of E- or Z-isomers is arbitrary as each gives >98% retention.1 The reactions shown so far do not include carbon nucleophiles. 

The benzoyl acid ester CD is an important intermediate in CD modification. Selecting the appropriate nucleophile (iodide, azide, thio-amyl acetate and hydroxylamine, alkyl amines) to attack the carbon atoms which connect with tosyl, can trigger nucleophilic substitution reaction. Then, series of functional CD sulfonate derivatives can be obtained. 

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