Lewis acid-promoted cyclization/halogenation of allenyl ethenetricarboxylates and the corresponding amides: stereoselective synthesis of haloalkenyl five-membered heterocycles

Abstract

Lewis acid-promoted intramolecular reactions of allenyl ethenetricarboxylates and the corresponding amides have been examined. Reactions of allenyl ethenetricarboxylates and the amides with Lewis acids such as AlCl3, AlBr3 and ZnX2 (X = Cl, Br, I) gave 3,4-trans haloalkenyl five-membered heterocycles stereoselectively. The stereochemistry was determined by NOE experiments and reduction of the cyclized products. Various transformations of the haloalkenyl functionalized cyclic compounds have also been performed.

Catalytic Cycloisomerization of Enyne Diesters Derived From 2‐Propargyloxyarylaldehydes

“…[1][2][3][4][5][6] The requisites of this type of cyclization are an electrophilic alkene (such as diethyl 2-arylidene malonate) bearing coordination site for metal halides and an alkyne which acts as the nucleophile. While the analogous ene-ene cyclization [7][8][9][10][11][12][13][14][15][16] is facile, enyne cyclization is less facile due to low nucleophilicity of alkyne and thus often requires highly electrophilic olefin containing three electron-withdrawing groups. Snider et al showed that in the presence of stoichiometric amount metal halide containing nucleophilic ligand such as FeCl 3 , enyne triester of type 1 undergoes intramolecular cyclization to compound 2 (Scheme 1a).…”

“…The requisites of this type of cyclization are an electrophilic alkene (such as diethyl 2‐arylidene malonate) bearing coordination site for metal halides and an alkyne which acts as the nucleophile. While the analogous ene‐ene cyclization [7–16] is facile, enyne cyclization is less facile due to low nucleophilicity of alkyne and thus often requires highly electrophilic olefin containing three electron‐withdrawing groups. Snider et al.…”