Palladium-Mediated Cyclization on Carbohydrate Templates. 2. Synthesis of Enantiopure Tricyclic Compounds
作者:Jean-Flaubert Nguefack、Véronique Bolitt、Denis Sinou
DOI:10.1021/jo970817j
日期:1997.10.1
The bromo substituted unsaturated carbohydrates 3a-f were prepared from 3,4,6-tri-O-acetyl-D-glucal by Ferrier reaction with the appropriate allylic or homoallylic alcohol, deacetylation followed by monosilylation with TBDMSCl, and then alkylation with BrCH2CBr=CH2. The N- and C-analogues 4a,b were synthesized by palladium alkylation of the intermediate carbonate with TsNHCH2CBr=CH2 and (MeO2C)(2)CHCH2CBr=CH2, respectively. Treatment of the unsaturated carbohydrates 3a, 4a, and 4b with a catalytic amount of Pd(OAc)(2)/PPh3 in CH3CN/H2O, in the presence of Bu4NHSO4 and NEt3, afforded the tricyclic compounds 5, 6, and 7, respectively. Under the same conditions, the analogue tricyclic compounds 8, 9, and 10 were formed starting from 3b-d. In the case of compounds 3e and 3f, the formation of the bicyclic glucal 11 via an already described beta-alkoxyelimination was only observed. Moreover, trapping of the sigma-alkylpalladium intermediate obtained from 3e with an external nucleophile yielded the 2-deoxy carbohydrate 12 and the 2,3-unsaturated sugar 13, using respectively sodium formate and sodium tetraphenylborate.