En route to thromboxane compounds from carbohydrates, I. Synthesis of the unsaturated sugar precursors

Allyl 4‐C‐[(carboxamido)‐ and (ethoxycarbonyl)methyl]hex‐2‐enopyranosides 18a–c, representing chiral precursors for the carbohydrate‐based construction of the ring systems of thromboxane A2 and B2 were prepared by means of the Claisen‐type rearrangement of the suitably substituted hex‐3‐enopyranosides 7a, b. The latter sugars were synthesized from allyl α‐D‐glucopyraoside (9) by modification of known procedures, including selective O‐benzoylation with 1‐(benzoyloxy)‐1H‐benzotriazole (11), and Tipson‐Cohen sulfonyl ester elimination of the 3,4‐di‐O‐mesylates 16 and 17. Studies on the corresponding methyl glycosides 8a–c showed a reduced stability of the 6‐O‐(tert‐butyldiphenylsilyl) ether group under the Tipson‐Cohen reaction conditions.