Catalytic Rhodium-Mediated Tetraene Carbocyclizations

James M. Takacs, Edward C. Lawson

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Abstract

Certain rhodium complexes ([RhCl3‒2 Ar3P], {[(1,5-COD)RhCl]2‒2 Ar3P}, (Ph3P)3RhCl, [(Ph3P)2Rh(NBD)]PF6) catalyze the cyclization‒amine trapping of the prototypical tetraene 8. The chemical yields are quite acceptable, up to 89% when one takes into account the unreacted tetraene recovered in reusable form. The best conversion is obtained in 2,2,2-trifluoroethanol (TFE, 75 °C) using RhCl3 as the catalyst precursor. The stereochemistry of the products obtained via rhodium catalysis complements that obtained with palladium. The cyclization of 8, promoted by the combination [RhCl3‒2 Ph3P] in TFE (75 °C), affords the morpholine-trapped cyclopentane (67%) bearing a cis relative stereochemistry between the side chains and predominantly the Z geometry within the newly formed side chain (i.e., a mixture of 9a (minor component) and 9b (major component)). In contrast, palladium catalysis affords predominantly the trans-cyclopentane derivative 9c. The cyclization of 8, promoted by the combination [RhCl3‒2 (p-Me2N-C6H4)3P] in TFE (75 °C), affords the morpholine-trapped cyclopentane 12 (63%), an isomer that may arise via the double-bond isomerization of 9a,b. Rhodium-catalyzed cyclization and trapping by N-benzylmethylamine affords predominantly cis-13a (R1 = CH2Ph, R2 = Me, 81%), and the reaction with diethylamine gives a 1:1 cis‒trans mixture of 13b (R1 = R2 = Et, 70% based on recovered 8). Attempts to cyclize and trap tetraene 8 with benzylamine, diisopropylamine, phthalimide, and N-methyl-p-toluenesulfonamide were unsuccessful under the conditions of [RhCl3‒2 Ph3P] catalysis in TFE.

Original languageEnglish (US)
Pages (from-to)4787-4793
Number of pages7
JournalOrganometallics
Volume13
Issue number12
DOIs
Publication statusPublished - Dec 1 1994

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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