1,3,4-Triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene - applications of a stable carbene in synthesis and catalysis

Conjugate‐Addition Organopolymerization: Rapid Production of Acrylic Bioplastics by N‐Heterocyclic Carbenes

“…This single‐addition product resembles those enamines derived from the 1:1 addition of TPT to more highly (doubly) activated Michael acceptors 12. 24…”

NHC‐Catalyzed Hydroacylation of Styrenes

“…[13] Recently, we designed a family of novel NHCs bearing a 2,6-dimethoxyphenyl moiety. [14] We hypothesized that these electron-rich NHCs would result in increased nucleophilicity of the Breslow intermediate [15,16] and would thus be suitable for the challenging hydroacylation of styrenes. Starting with the slightly activated p-cyanostyrene (2 a) under the conditions employed for the hydroacylation of cyclopropenes, [9b] we were pleased to obtain the linear and branched hydroacylation regioisomers l-3 a and b-3 a, respectively.…”

Conjugate‐Addition Organopolymerization: Rapid Production of Acrylic Bioplastics by N‐Heterocyclic Carbenes

“…The enamine 1 has been characterized spectroscopically by NMR [22] analysis and structurally by Xray diffraction analysis. [23] The molecular structure of 1 (Scheme 1) clearly displays a C = C double bond formed between C1 and C4 having a bond distance of 1.353 (2) . This single-addition product resembles those enamines derived from the 1:1 addition of TPT to more highly (doubly) activated Michael acceptors.…”

“…This single-addition product resembles those enamines derived from the 1:1 addition of TPT to more highly (doubly) activated Michael acceptors. [12,24] Possible mechanistic scenarios for the remarkable abovedescribed selectivity of the NHC structure for each of the three types of reactions involving a,b-unsaturated esters, including single addition, dimerization, and polymerization, are outlined in Scheme 2. On the basis of the results available to date, [14] it appears that dimerization (path a, Scheme 2) is unique to the triazolylidene carbene TPT, the least nucleophilic NHC in the series, and to linear (meth)acrylates, as we found no dimerization for methylene butyrolactones with a fixed s-cis conformation.…”

“…Received: November 14, 2011 Published online: January 23,2012 . Keywords: N-heterocyclic carbenes · organocatalysis · polymerization · polymers · renewable resources…”