Enamides are contained in many natural products such as salicylihalamide [1] and lobatamide, [2] and have recently been synthesized using transition-metal catalysts, as represented by a) the vinylation of amides, [3] b) the chelation-assisted coupling reaction of N-vinylamides with 1,3-butadiene, [4] c) the addition of amides to alkynes, [5] d) the oxidative amidation of alkenes, [6] and e) the isomerization of N-allylamides. [7] Dienamides are also important building blocks for preparing several alkaloids by the Diels-Alder reaction.[8] However, there are still few examples of transition-metal-mediated or -catalyzed synthesis of dienamides. [9] In considering potential new methods for the synthesis of enamides and dienamides, we have focused our efforts on ruthenium-catalyzed regio-and stereoselective codimerization reactions. Many examples of transition-metal-catalyzed codimerization reactions of alkenes with alkynes have been reported.[10] We also have already developed and reported the reactions of [2+2] cycloaddition [11] and linear codimerization reactions [12] of alkenes with alkynes. In sharp contrast, a codimerization reaction of "different alkenes" is still quite difficult except for hydrovinylation [13] and a challenging subject in modern organic and organometallic chemistry.[14]Herein we report zero-valent ruthenium-catalyzed codimerization reaction of different alkenes, that is, a codimerization reaction of N-vinylamides with alkenes as well as a cooligomerization reaction of N-vinylamides, acrylates, and ethylene, which offer novel and atom-economical methods for the synthesis of enamides with high regio-and stereoselectivity in one step. [15,16] As expected, the present catalyst system can be applied to the codimerization of N-vinylamides with alkynes, which enables the selective synthesis of dienamides.Treatment of N-methyl-N-vinylacetamide (1 a, 1.1 mmol) with ethyl acrylate (2 a, 1.0 mmol) in the presence of a catalytic amount of [Ru(h 6 -cot)(h 2 -dmfm) 2 ] (0.020 mmol; cot = 1,3,5-cyclooctatriene, dmfm = dimethyl fumarate) in N,N-dimethylacetamide (DMA, 3.0 mL) [14b, 17] at 160 8C for 3 h gave the linear codimer, ethyl 5-(N-methylacetylamino)-pent-4-enoate (3 a), in 90 % yield with 95 % E selectivity [Eq. (1) The reaction in Equation (1) required a temperature of over 150 8C for complete conversion of both substrates, and the best result was obtained at 160 8C (3 a, 90 %). However, at 170 8C, the reaction became sluggish, and the yield of 3 a decreased to 65 %.Several enamides were prepared by this method in good to high yields with high E selectivity [Eq. (2)]. Electrondeficient alkenes are suitable for this reaction; for example, codimerization of N-methyl-N-vinylacetamide (1 a) with ethyl vinyl ketone (2 c) or dimethyl maleate (2 d) gave 3 c and 3 d in respective yields of 70 % and 76 %. Although 2-norbornene (2 e) and ethylene (2 f) could also be used, the yields of the codimers, 3 e (exo only) and 3 f, were rather low. For the

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Heads you win: An unusual head‐to‐head dimerization of styrenes has been developed using the zero‐valent ruthenium catalyst [Ru(η6‐cot)(η2‐dmfm)2] (cot=1,3,5‐cyclooctatriene, dmfm=dimethyl fumarate) in the presence of primary alcohols to give the homo‐dimer in high regio‐ and stereoselectivity. The catalyst system is also effective for the selective co‐dimerization of styrenes with ethylene to give the co‐dimer in high yield.

A linear codimerization of 2-norbornenes with acrylic compounds such as acrylates and an acrylamide proceeded efficiently by ruthenium catalyst systems, RuCl3(tpy)/Zn (tpy = 2,2':6',2' '-terpyridine) or [RuCl2(C6H6)]2/Zn in a primary or secondary alcoholic solvent, to afford the corresponding exo-trans-2-norbornylacrylates as major products regio- and stereoselectively along with a small amount of cis isomers. The reaction of 2,5-norbornadiene with methyl acrylate also gave the linear exo-trans codimer, which was effectively catalyzed by the addition of triarylphosphines to the RuCl3(tpy)/Zn catalyst system.

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