Azides from sulfonate esters

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... 

With both building blocks 103 and 109 in hand, the total synthesis of lb was completed as shown in Scheme 17. Coupling of acid 103 and alcohol 109 under Yamaguchi conditions to give ester 110 and subsequent desilylation followed by chemoselective oxidation provided hydroxy acid 111. Lactonization of the 2-thiopyridyl ester derived from 111 in the presence of cupric bromide produced the macrodiolide 112 in 62% yield, which was finally converted to pamamycin-607 (lb) via one-pot azide reduction/double reductive AT-methylation. In summary, 36 steps were necessary to accomplish the synthesis of lb from alcohols 88 and 104, sulfone 91, ketone 93, and iodide rac-97. 

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