Neophyl rearrangement

Scheme 16 The neophylic rearrangement in the synthesis of 3-aryl piperidines...

A competing neophyl rearrangement to MeC (OCOPr)-CH2Ar had to be corrected for. 

In recent years, radical aryl migrations have received increased attention within the synthetic organic chemistry community. Yet, these reactions are also found as key steps in complex natural product synthesis [78]. For example, the neophyl rearrangement-which is the 1,2-phenyl migration of the neophyl radical 42 to form the tertiary radical 44 (probably via spirocyclohexadienyl radical 43)-was discovered by Urry and Kharasch more than 60 years ago (Scheme 13.9) [79], since which time numerous reports on neophyl-type rearrangements have been presented [80]. However, despite these efforts the postulated intermediate 43 has not yet been identified [81], The slow neophyl rearrangement (k = 762 s at 25 °C, [82]) can be used as a radical clock [83], The 1,2-aryl migration can also occur from C- to... 

O-centered radicals, and subsequently is referred to as the O-neophyl rearrangement [84]. 

Copper-catalysed trifluoromethylation-initiated radical 1,2-aryl migration (neophyl rearrangement) in a,a-diaryl allylic alcohols to give a-aryl / -trifluoromethyl ketones occurs with preferential migration of electron-deficient aryl groups over electron-rich ones, supporting a radical mechanism which has been confirmed by density functional calculations (Scheme 120). ... 

Urry and Kharasch s pioneering discovery of the neophyl rearrangement arose from an investigation into the factors influencing the course and mechanism of Grignard reactions (6). 

The neophyl rearrangement must proceed through a spiro [2.5]... 

Wilt, J.W, Kostruic, J.M., and Orlowski, R.C., Ring-size effects in the neophyl rearrangement. V. The carbenoid decomposition of 1-phenyl-cycloalkane-carboxaldehyde tosylhydrazones, /. Org. Chem., 30, 1052,1965. 

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