Grignard reagents with oxygen

Chemiluminescence is observed during the reactions of aryl Grignard reagents with oxygen 4650 or with aryl peroxides.4656 Analysis of the luminescence spectrum and e.s.r. data indicates that for the oxygen-induced reaction brominated biphenyls are the emitters, whereas in the peroxide case triphenylmethane is the luminescent species. 

Radicals on the carbon have been proposed in the reaction of Grignard reagents with oxygen Lamb, R.C. Ayers, P.W. Toney, M.K. Garst, J.F./. Am. Chem. Soc. 1966, 88,4261. 

The chemiluminescence of the reaction of Grignard reagents with oxygen was noted as early as 1906 [39], but only recently has some progress been made in understanding the mechanism of this reaction [40,41]. The following facts appear to be clearly established ... 

There is evidence of complexing of the Mg atom of the Grignard reagent with the carbonyl oxygen atom (76), and it is found that two molecules of RMgX are involved in the addition reaction, in some cases at least, possibly via a cyclic T.S. such as (77) ... 

Indeed, it is endothermic by over 130 kJmoU This documents that the polar/ionic bond between magnesium and oxygen is exceptionally strong, a fact we already surmised by the vigor of the reaction of Grignard reagents with air and water. 

The driving force for the reaction of Grignard reagents with a carbonyl compound is, as previously mentioned, the formation of the strong bond between magnesium and oxygen. As illustrated in Scheme l.l. this bond is formed in both the concerted and the stepwise reaction mechanisms. 

N-t-Butyldimethylsilylpyridinium triflate (45) reacts with Grignard reagents with almost complete regiospecifity to afford the corresponding 1,4-dihydropyridine derivatives which are easily oxidised by oxygen to give 4-substituted pyridines (46). ... 

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