ISSN:
0947-6539
Keywords:
asymmetric synthesis
;
carbohydrates
;
C-disaccharides
;
hetero-Diels-Alder reactions
;
thiazolyl oxabutadienes
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A method for the construction of substituted pyranoses by means of the hetero-Diels-Alder (HDA) reaction of ethyl vinyl ether with 1-oxabuta-1,3-dienes bearing a thiazolyl ring at C-2 is described. The cycloaddition with 1-(thiazol-2-yl)-2-penten-1-one (2) occurred with good endo/exo selectivity to give cis- and trans-3,4-dihydro-2H-pyrans 3a and 3b in a ca. 9:1 ratio and 91% overall yield. The elaboration of 3a through the conversion of the thiazole ring into the formyl group and reduction of the latter to alcohol, followed by hydroxylation of the double bond through hydroboration-oxidation led to the ethyl 2,3-dideoxypyranoside 8. The asymmetric version of this synthetic sequence started from the HDA cycloaddition of the same alkene with the chiral oxabutadiene 10 bearing the D-galacto-pentopyranosid-5-yl moiety at C-3. This reaction afforded a mixture of the four diastereomeric cycloadducts - 3,4-dihydro-2H-pyrans 11a,b and 12a,b - in 97% overall yield. The reaction was moderately endo and face selective. A high level of endo selectivity (96%) was obtained by the use of catalytic Eu(fod)3. The elaboration of the endo cycloadducts 11a and 12a by the same synthetic sequence as that developed for 3a (i.e. thiazolyl-to-formyl conversion and hydroxylation of the double bond) gave the uncommon C-disaccharides 15 and 16 featuring two directly linked pyranose rings.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19970030314
