Wen-Sen Li

A novel method for the mild and selective amidation of diesters and the amidation of monoesters

Abstract The selective monoamidation of diesters and amidation of esters mediated by Lewis acids are described. The selective amidations of dimethyl pyridine-2,5-dicarboxylate ( 1) and dimethyl 2,3-indole-dicarboxylate ( 4) with primary and secondary amines mediated by MgCl 2 or MgBr 2 under mild conditions gave the corresponding ester-amides in high yield.

Practical synthesis of the rebeccamycin aglycone and related analogs by oxidative cyclization of bisindolylmaleimides with a Wacker-type catalytic system

Abstract Using atmospheric O 2 as the stoichiometric oxidant, Pd 2+ /Cu 2+ -catalyzed oxidative cyclization of the corresponding bisindolylmaleimides provides the rebeccamycin aglycone and related indolo[2,3- a ]pyrrolo[3,4- c ]carbazoles in 58–88% yield. The method is operationally simple and utilizes readily prepared substrates, making the process amenable to scaleup.

Synthesis of substituted 2,3-dihydrobenzofuran in a process involving a facile acyl migration

Abstract Reduction of 2,6-diacetoxy-2′-bromoacetophenone ( 10 ) with NaBH 4 led to 3,4-diacetoxydihydrobenzofuran ( 12 ) in a process involving acyl migration followed by cyclization. Subsequent hydrogenolysis gave 4-acetoxydihydrobenzofuran which, upon saponification, afforded 4-hydroxydihydrobenzofuran ( 8 ) in good yield. This approach is shown to be a general method for preparation of substituted dihydrobenzofurans.

Electronic effects in the acid-promoted deprotection of N-2,4-dimethoxybenzyl maleimides

Abstract Cleavage of several 2,4-dimethoxybenzylmaleimides could be performed employing TFA in anisole. Electronic effects exemplified by varying the substitution present on the maleimide resulted in a variation in the rate of the deprotection. In contrast, 2,4-dimethoxybenzylsuccinimides were inert to the conditions.

A chemoselective, acid mediated conversion of amide acetal to oxazole: The key step in the synthesis of cardiovascular drug, ifetroban sodium

Abstract The cyclization of acetal amide was carried out with trimethylsilyl trifluoromethanesulfonate, followed by elimination using sodium methoxide to give 2,5-disubstituted oxazole, thus completing a new route to the cardivascular drug ifetroban sodium.

Fluoride-catalyzed Michael addition of nitrotoluenes to activated α, β-unsaturated esters

We have found that in the presence of fluoride ion, nitrotoluenes of type 1 undergo Michael addition to activated α, β-unsaturated esters of type 2 in good to excellent yield (Scheme 1). The generality and limitation of this reaction and its application to the chiral synthesis of benzazepine 4 are described.

Fluoride-catalyzed intramolecular denitrocyclization of nitrotoluenes to indanes

Abstract Fluoride-catalyzed Michael addition of nitrotoluenes to α,β-unsaturated esters followed by subsequent denitrocyclization to indanes is described.