Synthesis of 4-Deoxy Pyranosides via Catalyst-Controlled Site-Selective Toluoylation of Abundant Sugars.

A two-step procedure was developed for the synthesis of 4-deoxy pyranosides from the parent pyranosides with four hydroxy groups via organocatalytic site-selective acylation and reductive deacyloxylation.

Carboxylate Anions Accelerate Pyrrolidinopyridine (PPy)-Catalyzed Acylation: Catalytic Site-Selective Acylation of a Carbohydrate by in Situ Counteranion Exchange.

Acylpyridinium ions have been known as catalytically active species in acylation reactions catalyzed by 4-dimethylaminopyridine and its analogues. Acylpyridinium carboxylates were found to be 800-1300 times more reactive than the corresponding acylpyridinium chlorides. A catalytic cycle was developed, in which acylpyridinium carboxylates were generated by in situ counteranion exchange from the acylpyridinium chlorides. A catalyst loading as low as 0.01 mol % and catalyst turnover number of up to 6700 were achieved for site-selective acylation of a carbohydrate.

Organocatalytic Site-Selective Acylation of 10-Deacetylbaccatin III.

Organocatalytic site-selective diversification of 10-deacetylbaccatin III, a key natural product for the semisynthesis of taxol, has been achieved. Various acyl groups were selectively introduced into the C(10)-OH of 10-deacetylbaccatin III. The C(10)-OH selective acylation was also applied to acylative site-selective dimerization of 10-deacetylbaccatin III to provide the structurally defined dimer.