The first chemoselective tandem acylation of the Blaise reaction intermediate: a novel method for the synthesis of α-acyl-β-enamino esters, key intermediate for pyrazoles
作者:Yu Sung Chun、Ki Kon Lee、Young Ok Ko、Hyunik Shin、Sang-gi Lee
DOI:10.1039/b813369g
日期:——
The Blaise reaction intermediate, a zinc bromide complex of β-enamino ester, could be activated in situ by addition of a stoichiometric or catalytic amount of n-BuLi to allow chemoselective tandem C2-acylation providing α-acyl-β-enamino esters, which are valuable intermediates for the syntheses of tri- and tetrasubstituted pyrazoles.
practical protocol for the synthesis of fully substituted pyrazoles from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides in excellent yields under mild conditions is described. The transformation proceeds via an unusual [[3 + 3] - 1] pathway, which involves a formal [3 + 3] cascade cyclization followed by a spontaneous ring-contraction/sulfur extrusion reactionfrom 4H-1,3,4-thiadiazine intermediates