Dichlorocarbene electrophilic nature

The production of buta-1,3-dienes (37) by reaction of 1,2-diarylcyclopropenes with dihalocarbenes is thought to involve electrophilic attack of the carbene to give a dipolar intermediate (38).51 The addition of carbene to CO and H2C=0 has been studied by MNDO calculations.52 Photolysis of diethyl diazomalonate in a CO matrix at low temperature gave rise to ketenes by immediate trapping of the postulated carbene (39).53 The major products of reaction between dichlorocarbene and cyclone were CO and the gem-dichloro species (40).54 The predominance of this pathway over formation of the dichlorooxirane or the cyclopropane is attributed to the aromatic nature of the carbonyl ylide and its twist geometry. 

Two distinct scenarios arise for dichlorocarbene. First, the inductive withdrawal along crc cl bond lowers the electron density on the carbon to such an extent that the carbene is rendered largely electrophilic in nature. Second, a situation similar to that shown in 146 emerges and the electron pairs on chlorine atoms conjugate with the unfilled LUMO, leaving the filled HOMO to act as a nucleophile. It has been discovered from calculations that the former situation prevails over the latter, allowing dichlorocarbene to exhibit the electrophilic character largely [70]. 

In addition to phenolphthalein, other carboxy-substituted phenols have been subjected to the Reimer-Tiemann reaction. Mixtures of compounds, some lacking the carboxyl group, result (equation 6). Even though the nature of the reaction (i.e. the attack by the electrophilic dichlorocarbene on the nucleophilic... 

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