Abstract
Various bromo unsaturated carbohydrates 2−4 have been prepared from ethyl and aryl 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranoside by deacetylation, followed firstly by monosilylation with TBDMSCl and then by alkylation with 2-bromobenzyl bromide or 1-bromo-bromomethylcycloalkene. The N-, C-, and O-analogues 6−8 were prepared by palladium-mediated alkylation of the carbonate 5 with TsNHCH2−C6H4-o-Br, (CO2Me)2CH−C6H4-o-Br, and HOC6H4-o-I, respectively. The threo analogue 10 was obtained using the same methodology as for 2, after inversion of configuration at C-4 by means of a Mitsunobu reaction. Treatment of the unsaturated carbohydrates 2−4, 6−8, and 10 with a catalytic amount of Pd(OAc)2/PPh3 in DMF in the presence of Bu4NHSO4 and NEt3 afforded the annelated tricyclic compounds 11−13 and 15−18 in good yields when the anomeric substituent was the p-tert-butylphenyl group, via an intramolecular Heck reaction followed by a β-alkoxy-palladium elimination
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