Rearrangement metalla-Claisen

The stereochemical outcome was in agreement with the formation of a chelated allyl alkenylzinc compound that underwent a metalla-Claisen rearrangement with delivery of the allyl moiety anti to the homoallylic substituent. Although the stereocenter was more remote from the alkenylmetal, excellent induction was still observed152,153. 

Alternatively, nerolidol can be isomerised into farnesol, via a trisilylated tungstate (formally a metalla-Claisen rearrangement). The product is purified by distillation. [246] After its conversion into farnesyl chloride, this is treated with carbon dioxide and freshly precipitated barium, giving ( , )-homofarnesylic acid, which is finally reduced with lithium aluminium hydride. [247, 248]... 

The mechanism (Scheme 60) involves coordination of the terminal alkyne to the ruthenium atom followed by the formation of the vinylidene complex 135. Coordination of the allyl alcohol followed by addition of the alcohol to the ruthenium vinylidene complex leads to the ruthenium carbene complex 136. Metalla-Claisen rearrangement produces the jr-allyl-acylruthenium complex 137, which undergoes a reductive elimination to give the product 133 and regenerates the catalytically active ruthenium species. The regioselectivity of the coupling is independent of the site of ionization and the new bond formation occurs on the more substituted terminus of the double bond of the rr-allyl-ruthenium complex. 

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 . 

Vinylmagnesium bromide reacts as a Michael acceptor with a zincated hydrazone, yielding a 1,1-bimetallic species, which in some cases can be sequentially trapped with two different electrophiles.246 2463 The reaction proceeds via metalla-aza-Claisen rearrangement. The dimethyl hydrazone anion behaves as an azaallylic system (Scheme 81).247 Vinylphosphonium salts add Grignard reagents, forming alkylphosphonium ylides. These ylides... 

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