Diene cycloisomerization rhodium-catalyzed

Zhang54 published the first and only account of a non-asymmetric rhodium-catalyzed Alder-ene cycloisomerization of 1,6-enynes.55 The conditions developed by Zhang and co-workers are advantageous in that, similar to the ruthenium conditions developed by Trost, selectivity for 1,4-diene products is exhibited. The rhodium conditions are dissimilar from many other transition metal conditions in that only (Z)-olefins give cycloisomerization products. 

In contrast to nickel- and rhodium-catalyzed reactions, palladium cycloisomerizations of 1,6-dienes produce different isomers as the major products [62,63]. Palladium catalysts show a preference on electron-deficient alkenes for the... 

SCHEME 7.38 Seminal publication on rhodium-catalyzed cycloisomerization of 1,6-dienes. 

SCHEME 7.39 Selectivity of rhodium-catalyzed cycloisomerization of dienes. 

The reaction mechanism leading to advanced intermediate 85 starts with rhodium insertion into the aldehyde moiety. Rhodacycle formation follows to promote hydroacylation into the 4,6-diene providing cycloheptene compound 86. Then, rhodium catalyze a highly regioselective cycloisomerization reaction on the resulting triene to produce the final product 87 (Scheme 7.54 please refer also to Scheme 7.51). 

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