Organomagnesium compounds rearrangement

Organomagnesium compounds react with imines, prepared from 3-methoxy-2-naphth-aldehydes by a 1.4-addition mechanism. This reaction can be performed with high diastere-oselectivity. The method was applied for the synthesis of optically pure S-tetralones . Vinyhnagnesium bromide reacts as an acceptor with a ketone dimethyl hydrazone zincate 207, yielding a 1,1-bimetallic species, which can be reacted sequentially with two different electrophiles (equations 131 and 132) . The reaction proceeds via a metalla-aza-Claisen rearrangement, where the dimethylhydrazone anion behaves as an aza-allylic system . 

The intramolecular rearrangements of organomagnesium compounds containing one or more unsaturated sites has been an area of lively research effort. The work up through 1976 has been reviewed by Hill [2]. He summarizes the general features of the rearrangements ... 

Cyclization to an organomagnesium compound sufficiently less stable to be present only in small amounts at equilibrium, however, can lead to rearrangement. The organomagnesium-halide reagent either at the left or at the right in Eq. (u) forms a ca. 1 8 mixture of these reagents, by cyclization-cleavage. 

In addition to rearrangements in which one organomagnesium compound is converted to another, rearrangements may occur in the process of formation of the organometallic, or in the course of reaction of the organometallic with another reactant. In many cases, there is evidence that such rearrangements occur in a free-radical intermediate in the reaction. 

This rearrangement from isopropyl to n-propyl Grignard implies that any Grignard may be used to provide the intermediate subvalent titanium compound, and that addition of externally generated olefin would lead to the synthesis of organomagnesium compounds directly from olefins, without the intermediate formation of alkyl halide. 

The following paragraphs will deal with rearrangements observed in allylic organomagnesium compounds. 

Transition-metal compounds also catalyze the rearrangement of organomagnesium... 

The fairly recent literature has included a review of the preparation and reactions of allyl and butenyl Grignard reagents (5), a review of the reactions of allylic organometallic compounds (II), and a review of organomagnesium rearrangements, in which allylic derivatives were discussed in some detail (29). Since more recent publications do not appear to include new information that would significantly modify earlier conclusions, the previous discussions should suffice. 

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