Metathesis ruthenium-catalyzed enyne

Table 3. Ruthenium-catalyzed enyne metathesis Substrates Time Products Yields (%)...

Undheim [24] described the stereoselective synthesis of cyclic 1-amino-l-carboxylic acid using ruthenium-catalyzed enyne metathesis. His plan is shown... 

A total synthesis of (—)-stemoamide is achieved from (—)-pyroglutamic acid using ruthenium-catalyzed enyne metathesis as a key step in 14 steps in 9% overall yield [Eq. (6.79)]... 

Besides enyne metathesis [66] (see also the chapter Recent Advances in Alkenes Metathesis in this volume), which generally produces 1-vinylcyclo-alkenes, ruthenium-catalyzed enyne cycloisomerization can proceed by two major pathways via hydrometallation or a ruthenacycle intermediate. The RuClH(CO)(PPh3)3 complex catalyzed the cyclization of 1,5- and 1,6-enynes with an electron-withdrawing group on the alkene to give cyclized 1,3-dienes, dialkylidenecyclopentanes (for n=2), or alkylidenecyclopentenes (for n= 1) [69,70] (Eq. 51). Hydroruthenation of the alkyne can give two vinylruthenium complexes which can undergo intramolecular alkene insertion into the Ru-C bond. 

Kinoshita, A., Mori, M. Ruthenium catalyzed enyne metathesis. Syrr/etf 1994,1020-1022. 

Kinoshita, A., Mori, M. Total Synthesis of (-)-Stemoamide Using Ruthenium-Catalyzed Enyne Metathesis Reaction. J. Org. Chem. 1996, 61, 8356-8357. 

Since the 1990s, the olefin metathesis reaction has become a major synthetic tool in organic chemistry. Organoboranes were first employed in the construction of carbo-cyclic and heterocyclic alkenylboronates by ring closure of the corresponding acyclic precursors [104], Ruthenium-catalyzed enyne metathesis of acetylenic boronates was later demonstrated as a concise route for the construction of cyclic 1,3-dienylboronic esters, which can be further engaged in [4-i-2] cycloadditions (Scheme 9.51) [86]. 

Kinoshita A, Mori M. Total synthesis of (—)-stemoamide using ruthenium-catalyzed enyne metathesis reaction. J. Org. Chem. 1996 61 8356-8357. 

Renaud J, Graf CD, Oberer L. Ruthenium-catalyzed enyne metathesis of acetylenic boronates a concise route for the construction of cyclic 1,3-dienylboronic esters. Angew. Chem. Int. Ed. 2000 39 3101-3104. 

Kinoshita A, Sakakibara N, Mori M. Novel 1,3-diene synthesis from alkyne and ethylene by ruthenium-catalyzed enyne metathesis. 7. Aw. Chem. Soc. 1997 119 12388-12389. 

Grubbs et al. reported that the ruthenium-catalyzed RCM of a conjugated diene proceeds in such a way that the less hindered olefin moieties participate in the reaction. Consequently, RCM of 115 gives exo-methylene compound 116, and not exo-vinyl compound 117 (Scheme 24) [105]. This regioselectivity is complementary to that observed for enyne metathesis of 118, which gives exclusively 117 (Scheme 24) [106a]. 

It has been shown that ruthenium carbene complex lb developed for olefin metathesis can catalyze RCM of enynes. Using this catalyst lb, five- to nine-membered ring compounds 3 are synthesized from enyne 2 (Scheme j) i Sa-iSc The reaction procedure for RCM of an enyne is very simple. A benzene solution of enyne 2b is stirred in the presence of 1 mol% of ruthenium carbene complex lb at room temperature (RT) under argon gas to give cyclic compound 3b having a diene moiety. 

A palladium-catalyzed intramolecular benzannulation of bis-enynes 1135 proceeds chemoselectively to afford dihydroisocoumarins 1136 (Equation 441) <2002JOC2653>. A reaction sequence involving ruthenium-catalyzed yne-ene cross-metathesis of a polystyrene supported undecynoic acid ester followed by a Diels-Alder cycloaddition reaction with DMAD provides the basis for a combinatorial approach to dihydroisocoumarins featuring a variety of side chains at C-6 and C-8 <1999SL1879>. 

Polymer-supported synthesis of 1,3-dienes by efficient ruthenium-catalyzed in-termolecular enyne metathesis has been reported by Schiirer and Blechert [99]. The polystyrene resin, containing a propargyl ester moiety, was reacted with functionalized alkene in the presence of Cl2(PCy3)2Ru(=CHPh). The dienes obtained were cleaved from the polymer support using a paladium-catalyzed reaction with different nucleophiles (Eq. 57). 

The total synthesis of polycyclic alkaloid (-)-stemoamide was achieved in the laboratory of M. Mori via a ruthenium carbene catalyzed enyne metathesis. The cyclization was effected by 5 mol% of catalyst in benzene at 50 °C. After 11h of stirring under these conditions, 87% of the 5,7-fused bicyclic system was formed. 

Semeril, D., Bruneau, C., Dixneuf, P. H. Imidazolium and imidazolinium salts as carbene precursors or solvents for ruthenium-catalyzed diene and enyne metathesis. Adv. Syn. Catal. 2002, 344, 585-595. 

Non-carbenoid, ruthenium-catalyzed intramolecular enyne metathesis shares a mechanistic resemblance to the Pd-mediated reactions above. 

It has been demonstrated that these ruthenium complexes are also effective precatalysts for hydrogenation reactions. In 2001, Louie et al. reported the first example of ruthenium-catalyzed tandem RCM/hydrogenation and RCEM/hydrogenation (Scheme 5.1) [1]. Tandem RCM/isomerization [2], RCM/Kharasch addition [3], RCM/dihydroxylation [4], enyne metathesis/Claisen rearrangement [5], enyne metathesis/cyclopropanation [6], ROMP/hydrogenation [7], and CM/aza-Michael addition [8] have also been developed successfully. 

Mori M, Tonogaki K, Nishiguchi N. Syntheses of anolignans A and B using ruthenium-catalyzed cross-enyne metathesis. J. Org. Chem. 2002 67 224- 226. 

Saito N, Masuda M, Saito H, Takenouchi K, Ishizuka S, Namekawa J, Takimoto-Kanrimura M, Kittaka A. Synthesis of 24,24-ethanovitanrin D3 lactones using ruthenium-catalyzed intermolecular enyne metathesis potent vitanrin D receptor antagonists. Synthesis 2005 2533 2543. 

The allenylidene-mthenium complexes I also catalyze the enyne metathesis to alkenylcydoalkenes with a 1,3-diene stmcture. Initial studies showed the transformation of simple enynes with ether function [37] (Scheme 8.5). This reaction was significantly accelerated by initial catalyst photodiemical activation, which is now understood to favor the rearrangement of the allenylidene- into the active indenylidene-ruthenium moiety and arene displacement. 

Scheme 8.5 Enyne metathesis catalyzed by the photochemically activated ruthenium allenylidene precursor la.

Actually, applications of indenylidene-ruthenium complexes for alkene metathesis were reported before, at a time when the action mode of their ruthenium allenylidene precursors was not known. These complexes catalyzed a variety of RCM reactions of dienes and enynes [31, 32, 47] (see Section 8.2.2). 

Most of these catalytic systems are able to dimerize either aromatic alkynes, such as phenylacetylene derivatives, or aliphatic alkynes, such as trimethylsilylacetylene, tert-butylacetylene and benzylacetylene. The stereochemistry of the resulting enynes depends strongly on both the alkyne and the catalyst precursor. It is noteworthy that the vinylidene ruthenium complex RuCl(Cp )(PPh3)(=C=CHPh) catalyzes the dimerization of phenylacetylene and methylpropiolate with high stereoselectivity towards the ( )-enyne [65, 66], and that head-to-tail dimerization is scarcely favored with this catalyst. It was also shovm that the metathesis catalyst RuCl2(P-Cy3)2(=CHPh) reacted in refiuxing toluene with phenylacetylene to produce a... 

Storm, C., and Madsen, R. 2003. Enyne metathesis catalyzed by ruthenium carbene complexes (review of alkyne metathesis reactions). Synthesis 1—19. 

---