| Research Abstract |
A transition metal-catalyzed carbon-carbon bond formation reaction is one of the most advantageous method for the stereo- and enantioselective construction of cyclic compounds. In order to develop a new useful methodology for the asymmetric synthesis of five-membered compounds, we have studied palladium-catalyzed asymmetric cycloisomerization of readily available 1,6-enyes with chiral phosphine ligands or chiral sulfinyl functionality.
1. The palladium-catalyzed asymmetric cycloisomerizations of 1 , 6-enyes with chiral phosphine ligands produced optically active cyclopentane derivative with rather high enantioselectivity. The use of a chiral ferrocenyl phosphine as a ligand provided highest enantioselectivity.
2. The palladium-catalyzed reactions of l, 6-enyes bearing chiral sulfinyl groups at the appropriate sites in the olefinic parts gave cycized compounds, 1,4-dienes and 1,3-dienes with rather high enantiomeric excess. It should be noted that the stereoselectivity, production ratios of the 1,4-dienes to the 1,3-dienes, was dependent upon the steric envilonment around the sulfinyl groups. The plausible mechanis is proposed to rationalize the stereochemical results.
3. The palladium-catalyzed reactions of 1,6-enyes bearing chiral sulfinyl groups at the sites in the acetylenic parts produced exclusively 1,4-dienes with rather low e.e.. The steric results are rationalized by the formation of palladacycic intermediates.
4. Introduction of carboxyl functions into l, 6-enye substrates enhanced enantiocontrol, presum ably due to the conformational fixation of the intermediary palladacycles.
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