Methyl selective methanesulfonylation

The importance of sugar sulfonates as synthetic intermediates has been widely recognized.77,78 Selective methanesulfonylation and p-toluenesulfonylation of maltose and its derivatives has been studied. Umezawa and coworkers used sequential p-toluenesulfonylation and acetylation to obtain crystalline l,2,3,2, 3, 4 -hexa-0-acetyl-6,6 -di-0-p-tolylsulfonyl-/3-maltose in 45% yield.79 Dimolar methanesulfonylation of methyl /3-maltoside followed by acetylation afforded crystalline methyl 2,3,2, 3, 4 -penta-0-acetyl-6,6 -di-0-(methylsulfonyl)-/3-maltoside. The mother liquor also yielded a small proportion of a... 

Pyrolysis or photolysis of methanesulfonyl azide in 2-methyl butane (RH) produces formal C H insertion adducts attributed to reactions of the thermally generated nitrene. The selectivity of this nitrene for 3°/2°/l° C—H bonds was 6/2.3/1.0 Sulfonyinitrenes, like acylnitrenes, insert into the OH bonds of alcohols. 

Hydroboration of the methyl enol ether in (275) and subsequent oxidation provided crystalline (276). The selective hydrolysis of the protected lactol followed by treatment with methanesulfonyl chloride generated the sensitive dihydropyran (277), which was treated directly with osmium tetraoxide to give (278) and (279). 

The partial hydrolysis of 4a with methanolic potassium hydroxide followed by selective carboxylic acid reduction with excess borane and treatment of the resulting monoalcohol with methanesulfonyl chloride affords methyl 4-0-methanesulfonyl-2,3-0-isopropylidene-L-threonate (43). Facile displacement of the mesylate with azide followed by ester hydrolysis and catalytic reduction to an amine provides 4-amino-4-deoxy-2,3-0-isopropylidene-L-threonic acid (44). Mild acidic deprotection and ion-exchange desalting of 44 yields (2i ,3 S)-4-amino-4-deoxy-L-threonic acid (45), which has been utilized for the preparation of anthopleurine 46, the alarm pheromone of the sea anemone Anthopleura elegantissima [4] (Scheme 11). 

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