Die Dien-Addition an Ethyl-4,6-di-O-acetyI-2,3-didesoxy-a-~-ery~~ro-hex-2-enopyranosid (I) fuhrt ausschlieRlich zum a-D-manno-Addukt 2. Mit den Alkyl-2,3-didesoxy-a(~)-~-glycero-hex-2-enopyranosid-4-ulosen 3a und b entstehen je ein L-und o-eryfhro-Addukt 4a, b bzw. 5a, b. Diese tautomerisieren zu den D-und L-rhreo-Stereoisomeren 6a, b und 7b. Die Benzo[2,3]hexopyranosid-4-ulosen wurden mit NaBH, stereoselektiv zu Hexopyranosiden reduziert. Die Struktur von Methyl-2,3-didesoxy-l',2',3',6'-tetrahydro-4',5'-dimethyl-~-~~lyce~o-~f~~eo-benzo-[2,3]hexopyranosid-4-ulose (6b) wurde durch Rontgenstrukturanalyse bestimmt.
Cycloaddition with Unsaturated Carbohydrates, 111 I). -The Stereochemistry of the
Diels-Alder Reaction with Hex-2-enopyranoside and Hex-2-enopyranosid-4-ulosesThe dime addition to ethyl 4,6-di-0-acetyl-2,3-dideoxy-a-~-eryfhro-hex-2-enopyranoside (1) formed only the a-D-manno adduct 2. With alkyl 2,3-dideoxy-a(P)-~-giycero-hex-2-enopyranosid-4-doses 3a and b, the L-and D-eryfhro adducts 4a, b and 5a, b, respectively, are prepared. They tautomerize to give the D-and L-threo stereoisomers 6a, b, and 7b, respectively. The benzo-[2,3]hexopyranosid-4-uloses were reduced stereoselectively by NaBH, to hexopyranosides. The structure of methyl 2,3-dideoxy-l',2',3',6'-tetrahydro-4',5'-dimethyl-~-D-g~ycero-~-~hreo-benzo-[2,3]hexopyranosid-4-ulose (6 b) was determined by an X-ray analysis.