Rearrangements with Grignard reagents

The steroid epoxide rearrangement can occur with Grignard reagents only if both carbons of the epoxide ring are secondary. 

A similar type of transmetalation was also seen with l,2-dimethyl-5-trimethylstannylimidazole, which gave the 5-lithio derivative at -100°C, but rearranged to the 2-lithiomethyl derivative at higher temperatures [83JCS(P1)271]. However, transmetalation does not occur with Grignard reagents and 5-substituted imidazoles can be successfully prepared via this route (Scheme 49) (81 Mil 82OPP409). 

A new approach to this synthesis category involves the dimerization of halogenated oxime ethers 705 by reaction with Grignard reagents, where the C-2 atom of the product 706 arises from a rearrangement that is proposed to proceed via azirene intermediates <2002JA9032, 2004CL122>. 

In constrat to a-halo-/3-ketosulfoxides, I-chloroalkyl aryl sulfoxides react with Grignard reagents to give /3-oxido carbenoids. The rearrangement of these intermediates leads... 

The reactions of the isocyanurates have been reviewed previously (59HC(13)1, p.389). The following discussion will concentrate on three facets of isocyanurate chemistry ring cleavage, reactions with Grignard reagents and rearrangements. 

Rearrangement of several substituted chlorohydrins of fixed conformation has recently been reported by Curtin and Harder,3M and attention is directed to this interesting paper, since it is related to the abnormal reaction of a-haloketonos with Grignard reagents and hence pertinent to epoxide chemistry,... 

In the seoond, the halogen is displaced nucleophilically by nxygen and a transient epoxide species is formed which, in the presence of MgXg, rearranges to a carbonyl compound. The latter in turn reacts with Grignard reagent to give the observed products. A similar mechanism has been advanced by House 13-814 in a related problem (Eq. 167. ... 

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