No abstract

Iridium complex catalyzes an intramolecular ene-type reaction of 1,6-enynes to give cyclic 1,4-dienes. The reaction proceeds more efficiently in an imidazolium salt than in toluene and the ionic liquid can be reused.Transition metal-catalyzed cycloisomerization is an atomeconomical and powerful protocol for the synthesis of carbo-and heterocyclic systems. 1 Especially, an intramolecular ene-type reaction of enynes has been comprehensively studied and various transition metal complexes like Pd, 2 Pt, 3 Ti, 4 and Ru 5 ones are efficient catalysts. In these years, a series of Rh complex-catalyzed ene-type reaction of 1,6-enynes, possessing Z-olefinic moiety, has been reported. 6,7 We here disclose an Ir complex-catalyzed intramolecular ene-type reaction, where 1,6-enynes, having E-olefinic moiety, are more reactive substrates than Z-olefinic moiety. Moreover, an imidazolium salt was found to be a superior reaction media to conventional organic solvents.We chose allyl propargyl ether 1a, where the E/Z ratio of the olefinic moiety is 2:1, as a model 1,6-enyne and examined a cycloisomerization using iridium complex [IrCl(cod)] 2 in toluene (Table 1, entry 1). As a result, the substrate was completely consumed in eight hours at 90°C and an ene-type reaction proceeded to give cyclic 1,4-diene 2a in good yield. 8 Unlike Ir complex-catalyzed carbonylative coupling 9 and [2+2+2] cycloaddition, 10 the addition of phosphine ligands deactivated the Ir-catalyst in the ene-type reaction. For an example, Ir-DPPP complex 9b took longer reaction time to give product 2a in lower yield (entry 2). When the reaction was quenched at 3 hours, 30% of enyne 1a was recovered and the Z-isomer of 1a was dominant (entry 3). These results imply that the E-isomer reacted more promptly than the Z-isomer. Actually, enyne 1a, having E-olefinic moiety, was consumed only within three hours and the 1,4-diene 2a was obtained in higher yield of 82% (entry 4). 11 On the contrary, enyne 1a, having Z-olefinic moiety, gave much lower yield under the same reaction conditions (entry 5). Compound 1a-Z was completely consumed by longer reaction time, however, the yield did not reach that by 1a-E. The higher reactivity of the E-isomer of enyne than the Z-isomer in ene-type reaction was opposite to the case in the Rh complex-catalyzed reaction. 6,12

Carbonylation O 0305Iridium-Catalyzed Enantioselective Pauson-Khand-Type Reaction of 1,6-Enynes. -Intramolecular asymmetric Pauson-Khand reaction of various 1,6-enynes (I) and (IV) is efficiently catalyzed by an iridium-chiral tolBINAP complex. In some cases [e.g. (Ve) -(Vg)], a lower partial pressure of carbon monoxide (0.2 atm of CO and 0.8 atm of argon) gives better results. The iridium-tolBINAP complex also catalyzes the asymmetric Pauson-Khand reaction with cinnamaldehyde (VI) as carbonyl source. -(SHIBATA*, T.; TOSHIDA, N.; YAMASAKI, M.; MAEKAWA, S.; TAKAGI, K.; Tetrahedron 61 (2005) 42, 9974-9979; Dep. Chem., Waseda Univ., Tokyo 169, Japan; Eng.) -Mischke 03-058

2005 Furan derivatives R 0060Iridium Complex-Catalyzed Intramolecular Ene-Type Reaction of 1,6-Enynes Accelerated in Ionic Liquid. -The title reaction of (E)-configurated substrates represents the first example of transition metal catalyzed cycloisomerization in ionic liquid. It proceeds faster and affords the products in higher yields compared to toluene.-(SHIBATA*, T.; YAMASAKI, M.; KADOWAKI, S.; TAKAGI, K.; Synlett 2004, 15, 2812-2814; Dep. Chem., Sch. Sci. Eng., Waseda Univ., Shinjuku, Tokyo 169, Japan; Eng.) -Steudel 20-102