Rhodium N-Heterocyclic Carbene-Catalyzed [4 + 2] and [5 + 2] Cycloaddition Reactions

• Published in: Journal of organic chemistry 2006-01, Vol.71 (1), p.91-96
• Main Authors: Lee, Sang Ick, Park, Se Yeoun, Park, Ji Hoon, Jung, Il Gu, Choi, Soo Young, Chung, Young Keun, Lee, Bun Yeoul
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Cyclization; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Heterocyclic compounds with only one n hetero atom and condensed derivatives; Hydrocarbons - chemistry; Magnetic Resonance Spectroscopy; Methane - analogs & derivatives; Methane - chemistry; Molecular Structure; Organic chemistry; Preparations and properties; Rhodium - chemistry
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo051685u

A rhodium complex of N-heterocyclic carbene (NHC) has been developed for intra- and intermolecular [4 + 2] and intramolecular [5 + 2] cycloaddition reactions. This is the first use of a transition-metal NHC complex in a Diels−Alder-type reaction. For the intramolecular [4 + 2] cycloaddition reactions, all the dienynes studied were converted to their corresponding cycloadducts in 91−99% yields within 10 min. Moreover, up to 1900 turnovers have been obtained for the intramolecular [4 + 2] cycloaddition at 15− 20 °C. For the intermolecular [4 + 2] cycloadditions, high yields (71−99%) of the corresponding cycloaddition products were obtained. The reaction time and yield were highly dependent upon the diene and the dienophile. For the intramolecular [5 + 2] cycloaddition reactions, all the alkyne vinylcyclopropanes studied were converted to their corresponding cycloadducts in 91−98% yields within 10 min. However, the catalytic system was not effective for an intermolecular [5 + 2] cycloaddition reaction.