Unexpected reactivity of diaryl α-diketones with thiazolium carbenes: Discovery of a novel multicomponent reaction for the facile synthesis of 1,4-thiazin-3-ones
Diaryl α-diketones do not undergo polarity reversal in the presence of (benzo)thiazolium carbenes but are engaged in a novel multicomponent reaction with water to efficiently give medicinally relevant 1,4-thiazin-3-one heterocycles. Three different sets of conditions have been optimized to furnish the title compounds in fair to excellent yields depending on the electronic properties of α-diketone aromatic substituents and thiazolium or benzothiazolium substrate. A plausible reaction mechanism is also proposed based on the isolation and characterization of the postulated key intermediate and isotopic labeling experiments.
Formation and crystallographic elucidation of stable [4 + 2]-coordinate nickel(ii) N,S-heterocyclic carbene (NSHC) complexes
A series of square-planar N,S-heterocyclic carbene (NSHC) complexes trans-[NiX2(N-RBzTh)2] (BzTh = benzothiazolin-2-ylidene) (R/X = Bz/Br; Me/I; Et/I; Pri/I; Bui/I) have been synthesized and characterized by X-ray single-crystal diffraction analysis. These are the first crystallographically established NSHC complexes of nickel in the literature. The N,S-heterocyclic carbene (NSHC) rings invariably twist away from co-planarity with the metal coordination plane such that the N-substituent moves on top and below the metal to facilitate electrostatic γ-hydride interaction, thus giving an essentially [4 + 2] coordination at the Ni(ii) center. These compounds are active toward reductive Ullmann-type coupling reactions in Bu4NBr showing higher activities towards bromoanisole or bromotoluene than bromobenzene. The complex trans-[NiI2(N-Pr iBzTh)2] with the shortest Ni...H anagostic separation and a near-ideal orthogonal orientation between the carbene and metal planes gives the highest yields.
Ding, Nini,Zhang, Jun,Hor, T. S. Andy
experimental part
p. 1853 - 1858
(2009/08/08)
Selective Formation of Triose from Formaldehyde Catalyzed by Thiazolium Salt
In the self-condensation of formaldehyde catalyzed by thiazolium salts, dihydroxyacetone (triose), but not glycolaldehyde, was formed selectively and in high yield.This is of much interest as a facile and novel synthesis of triose from this C1 compound.A mechanism which can account for the selective formation of dihydroxyacetone is described.