Rhodium-mediated rearrangements rearrangement

Marsden, S. P., Pang, W.-K. Efficient, general synthesis of silylketenes via an unusual rhodium mediated Wolff rearrangement. Chem. Common. 1999, 1199-1200. 

The synthesis of bicyclo[3.2.1]octadienes 86 has been accomplished by refluxing divinyl-cyclopropanes 85 in xylene. Subsequent research led to the development of conditions employing a rhodium-catalyzed step for the synthesis of bridged systems via the cyclopropanation of cyclopentadienes, furans and pyrroles (see section on transition-metal-mediated rearrangements). 

An important factor in the efficiency of this reaction may well be complexation between the rhodium carbene and the bond into which carbene insertion is to take place certainly rhodium mediated C—H bond activation is known to take place. The addition to alkenes can also be catalysed " rearrangement of the product provides a useful route to cyclopentane rings. 

Several other examples of metal-mediated carbon skeleton rearrangements leading to cyclopropane products have been reported. " For example, the cyclopropanation of norbor-nadiene with rhodium or platinum catalysts gives cyclopropane-containing rearrangement products 12 and 13 in good yields. ... 

Rainer has studied the sulfonium ylide-mediated thio-Claisen rearrangement. Rhodium carbenoid 443, generated from rhodium acetate and alkenyl diazoacetate 441, reacted with the 2-ethylthioindole 440 to reveal the sulphur ylide 445. Proton shift generated the ketene aminethio acetal 446 which underwent thio-Claisen rearrangement to yield indoline 442 in excellent yield. 

A BASF group showed that rhodium-catalyzed reaction of a-(-)-pinene gives (-l-)-3-formylpinane (Scheme 4.53) [11]. In contrast, the use of Co2(CO)g led to the formation of (-)-2-formylbornane. The Wagner-Meerwein rearrangement is mediated by the intermediarily formed HCo(CO)4 with acidic properties. Prior isomerization of a- to P-pinene can be avoided by applying a high CO partial pressure and low temperatures. Based on this protocol and a subsequent reductive amination, chiral aminomethyl-plnane was prepared in the 100 g scale. 

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