Phenylseleno glycoside

As an alternative to the Bu3SnH-phenylseleno glycoside chemistry, radicals may also be generated by samarium diiodide reduction of anomeric arylsulfonyl groups [115], (R=Ph] (O Scheme 55). 

Accordingly, fully benzylated selenogalactoside 43 was selectively activated with NlS/TMSOTf in the presence of detuned phenylseleno glycoside acceptor 44... 

The pure major diastereomer 138 on / -elimination gave the dihydroxythiaglycal 139, which on electrophilic glycosidation using phenylselenyl chloride and silylated nucleobase provided the major a-phenylseleno-/ -anomer 140, along with a small amount of the / -phenylseleno-a-anomer. In a similar reaction, the iodo compound was obtained when PhSeCl was replaced with AT-iodosuccinimide (NIS) (Scheme 37). 

The final SnCl2-mediated glycosidation of the 2-phenylseleno glycosyl fluoride 267 and the alcohol 311 gave the oligosaccharide 312 with complete stereocontrol, which was subjected to Sinay s orthoester formation to afford everninomicin 13,384-1 (314) after successful deprotections, including reductive debenzylation and TBAF-induced desilylation. 

Two papers have reported on die addition of diphenyl diselenide to tri-O-acetyl-D-ghical and -D-gaiactal which gives rise to l-phenylseleno 2-azido-2-deoxy glycosides as rqiorted in Ch ter 10. See ref. 119 for a comment on phenyl seloioglycosides as glycosylating agents. 

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