Hydrative cyclization

Hydrative cyclization of diynes with ruthenium catalyst has been reported for the synthesis of sulfolenes or enones in aqueous medium.381 Reactions of unsymmetrical 1,6-diynes have been investigated, and some substrates are found to exhibit a directing effect of the ketone moiety in a pendant group. 

The hydrative cyclization involves the formation of a ruthenium vinylidene, an anti-Markovnikov addition of vater, and cyclization ofan acylmetal species onto the alkene. Although the cyclization may occur through a hydroacylation [32] (path A) or Michael addition [33] (path B), the requirement for an electron- vithdra ving substituent on the alkene and lack of aldehyde formation indicate the latter path vay to be the more likely mechanism. Notably, acylruthenium complex under vent no decarbonylation in this instance. 

When the double bond is conjugated with a carbonyl group, a different type of product is formed. In the presence of water a hydrative cyclization was performed by reaction of yne-enones, leading to cyclic 1,5-diketones in good yields by using the system CpRu(CH3CN)3PF6/camphorsulfonic acid as a catalyst. In anhydrous acetone, pyrans were produced in place of 1,5-diketones [77] (Eq. 56). 

Af-Benzyl-/V- (/V-o-methoxyphcnylcarbamoyl)mcthyl glycine (29) underwent de-hydrative cyclization to 4-benzyl-6-hydroxy-l-o-methoxyphenyl-3,4-dihydro-2(1 H)- pyrazinone (30) (l,r-carbonyldiimidazole, THF, 30 —> 65°C, 17 h 83% other reagents gave lower yields).487... 

Reaction of 1,6-diynes 414 and 415 with Pdl2, CO, and O2 in methanol followed by treatment with Et3N affords hi- and terthiophenes 416 and 417, respectively <1999T485>. 2,5-Dihydrothiophene 1,1-dioxide 419 is synthesized by Ru-catalyzed hydrative cyclization of diyne 418 (Equation 12) <20050L2097>. 

For example, l-benzoyl-2-(pyrid-2-yl)hydrazine (213), obtainable from the reaction of 2-hydrazinopyridines (212) with benzoyl chloride (57JCS727 66JOC251) or benzoic anhydride (59JOC1478), undergoes de-hydrative cyclization in boiling phenol (59JOC1478) or phosphoryl... 

Trost, B.M. and Huang, X. (2005) Ruthenium-catalyzed diyne hydrative cyclization synthesis of substituted 1,3-diene synthons. Organic Letters, 7, 2097-2099 Trost, B.M. and Huang, X. (2006) Synthesis of substituted 1,3-diene synthetic equivalents by a Ru-catalyzed diyne hydrative cyclization. Chemistry-An Asian Journal, 1, 469-478. 

Trost et al. reported the ruthenium-catalyzed het-ero-[4 + 2]-cycloaddition and hydrative cyclization of yne—enone 439 (Scheme 140).201 In the absence of water the reaction proceeds through the usual [4 + 2]-cycloaddition to give the bicyclic pyran 440, while the hydrative cyclization occurs in the presence of water to afford the cyclic diketone 441. The reaction is... 

Representative procedure for the gold-catalyzed hydrative cyclization of allenynes. (E)-(2-Methyl-2-styrylcyclopentyl)(phenyl)methanon ... 

Cyclizations can be initiated by a nucleophilic attack, e.g. by H2O or a carboxylic acid, to a catalytic ruthenium vinylidene followed by trapping with an electrophile. Lee and coworkers described the Ru-catalyzed hydrative cyclization of 1,5-enynes (Scheme 33) to give functionalized cyclopentanones [147]. Treatment of 1,5-enynes bearing an internal Michael acceptor with a catalytic amount of [Ru3Cl5(dppm)3]PF6 in the presence of water initially afforded the corresponding ruthenium vinylidene species. Nucleophilic anti-Markovnikov addition of water... 

Scheme 33 Ru-catalyzed hydrative cyclization of 1,5-enynes to cylopentanones /— [CpRu(CH3CN)3]PFe (5 mol%)...

The HgSO catalyzed hydrative cyclization of 1,6-heptadiynes was reported by Zhang et al. (2011). This reaction proceeded smoothly under the mild conditions for differently 4-sustituted 1,6-diynic substrates giving corresponding 3-methyl-2-cyclohexenones with high to excellent yields. The microwave-assisted aldol condensation of cyclohexenones under the catalysis of BiClg afforded 3-styryl-cyclo-hexenones. 

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