EFFICIENT ROUTES TO PYRANOSIDIC HOMOLOGATED CONJUGATED ENALS AND DIENES FROM MONOSACCHARIDES

Citation
Jc. Lopez et al., EFFICIENT ROUTES TO PYRANOSIDIC HOMOLOGATED CONJUGATED ENALS AND DIENES FROM MONOSACCHARIDES, Tetrahedron, 49(35), 1993, pp. 7701-7722
Citations number
61
Categorie Soggetti
Chemistry Inorganic & Nuclear
Journal title
ISSN journal
00404020
Volume
49
Issue
35
Year of publication
1993
Pages
7701 - 7722
Database
ISI
SICI code
0040-4020(1993)49:35<7701:ERTPHC>2.0.ZU;2-8
Abstract
Three new processes for the obtention of pyranosidic dienes type B, an d D and homologated conjugated enals A, have been designed in the cont ext of the preparation of useful chiral building blocks from monosacch arides. Addition of vinylmagnesium bromide onto ulose 1, followed by a cetal ring opening; benzoate protection at C-4 and C-6; and dehydratio n of the tertiary hydroxyl group, mediated by thionyl chloride, reveal s to be a straightforward route to diene 11. Analogous dehydration on conformationally rigid 2 was not regioselective and afforded isomeric dienes 3 and 6 in a 1:1 ratio. Addition of 2-lithio-1,3 dithiane onto locked 2,3-anhydropyranoses 21 and 22 followed by unravelling of the S ,S-acetal moiety led efficiently to homologated alpha-enals 26, 27, 31 , and 30 and hence to dienes 34, 14, 20 and 13 through Wittig methylen ation. Finally alpha-alkoxyvinyl ethers, prepared either by Wittig-Hor ner reaction of alpha-alkoxy-uloses, or by hetero Diels-Alder reaction of conjugated-enals, afforded in good to excellent yields pyranosidic alpha-enals 37, 42, 43, 44, 50 and 51 on treatment with pyridinium hy drochloride in pyridine or a mixture acetic acid-water (4:1).