The transition metal-catalyzed reaction of allenes has emerged as a useful protocol to prepare synthetically useful cyclic compounds with high levels of regio-and stereoselectivity.1 To control the selectivity of the cumulated π-bonds of the allenes, intramolecular reactions involving allenes are often reported. In this regard, cyclizations of bisallenes have been investigated to provide attractive bicyclic products (bicyclo[3.2.0] or bicycle[3.1.1] products), organometallic reagent (silicon, stannane, and germanium)-incorporated cyclic compounds, and steroid scaffolds.
2,3,4Although a range of transition metal-catalyzed cyclizations using bisallenes have been presented, there are no reports of reductive cyclization of 1,5-bisallenes initiated by the hydrometallation of the allene. Presumably, upon hydrometallation, the complicated regioselectivity and attenuated reactivity of the allene relative to the alkyne would result in a lack of research on the reductive cyclization of 1,5-bisallenes.There are a few reactions initiated by hydrometallation of allenes; 1) ring expansion of allenylcyclobutanols, 5 2) reductive aldol reaction of allenic esters, 6 and 3) reductive cyclization of allene-carbonyl compounds and allene-hydrazones.
†This paper is dedicated to Professor Eun Lee on the occasion of his honourable retirement. PCy 3 (10) To a premixed solution of PtCl2 (5 mol %), P(Ph-2,4,6-OMe3)3 (10 mol %), and SnCl2 (25 mol %) under H2 (1 atm) in dichloroethane was added the starting material under H2 (1 atm) at room temperature. The resulting mixture was allowed to run at 80 o C until the starting material was completely consumed.
Upon platinum‐catalyzed hydrogenation, allenynes underwent reductive cyclization to provide hetero‐ and carbocycles with completely controlled regio‐ and stereoselectivity. By employing hydrogen as a reductant, the use of stoichiometric amounts of toxic organometallic reductants was avoided, leading to clean and cost‐effective synthesis. A possible catalytic cycle is proposed on the basis of a deuterium‐labeling study and theoretical calculations.
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