Platinum catalysis cycloisomerizations

Zhang, L., Sun, J., Kozmin, S. A. (2006). Gold and platinum catalysis of enyne cycloisomerization. Advanced Synthesis Catalysis, 348, 2271-2296. 

Zhang, L., Sun, J. and Kozmin, S.A. (2006) Gold and platinum catalysis of enyne cycloisomerization. Advanced Synthesis Catalysis, 348, 2271-2296. Khramchikhin, V.A., Dogadina, A.V., Khramchikhin, A.V. and lonin, B.I. (2012) Heterocyclization reaction of chloroacetylenephosphonates with 2-acylamidomalonates into 5-(dialkoxyphosphorylmethylidene)oxazolines. Russian Journal of General Chemistry, 82(4), 776-778 Zhurnal Obshchei Khimii, 82(4), 694-696. 

Fiirstner and coworkers developed a new Pt- and Au-catalyzed cycloisomerization of hydroxylated enynes 6/4-141 to give the bicylo[3.1.0]hexanone skeleton 6/4-143, which is found in a large number of terpenes [317]. It can be assumed that, in the case of the Pt-catalysis, a platinum carbene 6/4-142 is formed, which triggers an irreversible 1,2-hydrogen shift. The complexity of the product/substrate relationship can be increased by using a mixture of an alkynal and an allyl silane in the presence of PtCl2 to give 6/4-143 directly, in 55 % yield (Scheme 6/4.36). 

Few examples of ene-yne cycloisomerization reactions are seen in the literature. The first results for ene-yne cycloisomerizations were with systems bearing an heteroatom (amine or oxygen) next to the alkene counterpart (forming an enamine or an enol ether). Indeed, Dake s group reported the cyclization of enesulfonamides on alkynes (69-70, Scheme 5.30) under catalysis by platinum and silver salts.85 Catalysis using AgOTf (1 1 mol%) was particularly efficient with systems such as 69 (Scheme 5.30)... 

Rhodium is a rare white-silvery metal classified as a member of the platinum group metals. As a result, rhodium is commonly used as a catalyst in chemical reactions. It is also used in several chemical feedstock processes, including hydroformylation. Furthermore, rhodium has been used to catalyze more complex processes, such as higher order cycloaddition reactions. In addition, rhodium has been used in simpler reaction types such as hydrogenation and cycloisomerization. The fact that rhodium is effective for a wide range of chemical processes makes it an attractive metal for catalysis. 

The utility of the platinum-catalyzed enyne cycloisomerization for the formal synthesis of Rosephilin, which is a member of prodiginine family of alkaloids, was reported by Trost and Doherty (Scheme 7.44) [94]. The critical step in the synthesis was the conversion of enyne 221 to bicyclic diene 222 by platinum-catalyzed enyne cycloisomerization. While palladium catalysis was found to be ineffective, the desired cyclopentene 222 was obtained when 221 was treated with the platinum-based catalytic system developed by Murai. Diene 222 was converted to tricyclic pyrrole intermediate 223 in an 11-step sequence. Since 223 had been converted to roseophilin 224, the entire procedure represented a formal synthesis of the alkaloid. 

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