Rhodium I -Catalyzed Carbocyclization Reactions

Transition metal-catalyzed carbocycUzation reactions of tethered diene, enyne, diyne, and vinylallene derivatives represent an important class of transformations in synthetic organic chemistry. This may be attributed to the abihty to significantly increase molecular complexity through the highly selective combination of acyclic components, thereby facilitating the synthesis of complex polycychc products. Recently, rhodium-catalyzed carbocyclization reactions have attracted significant attention due to their immense synthetic versatility and the unique selectivities observed over a range of different transformations. This chapter provides an account of recent developments in rhodium-catalyzed [4-1-2] and [4-i-2-t2] carbocyclization reactions. 

Matsuda and co-workers described the first intermolecular rhodium-catalyzed [4-1-2] reaction in 1987 [5]. Consistently with the other transition metal catalysts that had been developed for similar systems, the rhodium-catalyzed version was also limited to 

Modem Rhodium-Catalyzed Organic Reactions. Edited by P. Andrew Evans Copyright 2005 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30683-8 

Chung and co-workers have examined similar systems and have successfully employed a variety of trisubshtuted dienes (Eq. 1) [7]. These represent the first examples using both di- and trisubshtuted olefins. The addihon of three subshtuents at Rj, R3, and R4 (compare Tab. 12.1) allows for the instaUahon of up to five subshtuents this had not been previously examined using a rhodium catalyst. This system is also applicable to the corresponding intramolecular reachon, which is discussed later in this chapter (Sechon 12.2.2). 

These catalysts are among the first to exhibit the ability to catalyze the intermolecular [4+2] annulation over a broad range of substrates, requiring neither strongly electron-withdrawing nor donating functionahty. 

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