Ketones, methyl vinyl palladium catalyzed

Microwave promoted, palladium-catalyzed, DPPP-controlled arylation of butyl vinyl ether with 4-tert-butylphenyl triflate afforded the branched arylation product and the corresponding methyl ketone, indicating the occurrence of selective internal a-arylation. Addition of water to the reaction mixture and microwave-heating for 2.8 min at 55 W smoothly produced the hydrolyzed product, 4-tert-butylacetophe-none, with an isolated yield of 77% (Eq. 11.2) [17]. 

Palladium-catalyzed bis-silylation of methyl vinyl ketone proceeds in a 1,4-fashion, leading to the formation of a silyl enol ether (Equation (47)).121 1,4-Bis-silylation of a wide variety of enones bearing /3-substituents has become possible by the use of unsymmetrical disilanes, such as 1,1-dichloro-l-phenyltrimethyldisilane and 1,1,1-trichloro-trimethyldisilane (Scheme 28).129 The trimethylsilyl enol ethers obtained by the 1,4-bis-silylation are treated with methyllithium, generating lithium enolates, which in turn are reacted with electrophiles. The a-substituted-/3-silyl ketones, thus obtained, are subjected to Tamao oxidation conditions, leading to the formation of /3-hydroxy ketones. This 1,4-bis-silylation reaction has been extended to the asymmetric synthesis of optically active /3-hydroxy ketones (Scheme 29).130 The key to the success of the asymmetric bis-silylation is to use BINAP as the chiral ligand on palladium. Enantiomeric excesses ranging from 74% to 92% have been attained in the 1,4-bis-silylation. 

While simple unactivated cyclopropanes have yet to be used for [3 + 2] cycloaddition, Tsuji and coworkers have developed a palladium-catalyzed cycloaddition reaction using electron-deficient vinylcy-clopropanes. Thus, vinylcyclopropane (43) undergoes smooth cyclization with methyl acrylate in the presence of a palladium catalyst to give vinylcyclopentane (44) as a mixture of diasteroisomers (equation 35). The cycloaddition probably proceeds through the zwitterionic ( ir-allyl)palladium intermediate (45) and its stepwise reaction with the acrylate (equation 36). Enones such as cyclopentenone and methyl vinyl ketone will also react. Reaction of the same vinylcyclopropane with phenyl isocyanate produces vi-nyllactam (46) (equation 37).Some cycloaddition reactions with (cyclopropyl)Fp complexes have also been reported. However, the substrates are limited to SO2 and TCNE and the yields have not been disclosed (equation 38). ... 

Asymmetric [3 + 2] cycloaddition of 2-(sulfonylmethyl)-2-propenyl carbonate 56 with methyl acrylate or methyl vinyl ketone is also catalyzed by the palladium-ferrocenylphosphine 8b complex to produce methylenecyclopentane derivatives with up to 78% ee (Scheme 2-36) [52]. 

While alcohol oxidations have been the most common metal promoted reactions involving molecular oxygen, a number of other metal catalyzed oxidations of potential synthetic interest have been reported. Supported palladium catalysts are comparable to many soluble palladium catalysts in promoting the selective oxidations of alkenes and aromatics. 2-Butene was oxidized primarily to crotonic acid over Pd/C in water but methyl vinyl ketone and crotonaldehyde were also formed in significant amounts. When this oxidation was run in acetic acid the allyl acetates were the major products, particularly when a Pd/Al203 catalyst... 

Active methylene compounds can be added to polar double bonds such as those in acrylate esters and methyl vinyl ketone as has been described in the previous section. Active methylene compounds can also be added to carbon-carbon multiple bonds in allenes and alkynes with the aid of the transition metal complexes as the catalyst. The addition of methylmalononitrile to 3-phenyl-l,2-butadiene takes place in the presence of Pd2(dba)3-CHCl3 to give the corresponding addition product with E-stereochemistry (Eq. 67) [137 a]. The C-C bond formation occurs exclusively at the terminal position of the allenes. Trost et al. independently reported the similar results with respect to palladium-catalyzed addition of C-H bonds in active methylene compounds to allenes [137 b. ... 

Indole-3-carboxylate esters and 3-acetylindoles can be prepared by palladium-catalyzed cycli-zation of enamines (14). These can be prepared from the corresponding anilines by condensation with j8-dicarbonyl compounds or by palladium-catalyzed substitution reactions with ethyl acrylate or methyl vinyl ketone <86BCJ927, 90S215>. Overall yields for the two-step process are 60-80% (Scheme 33). 

Disubstituted isocoumarins arise from the copper(II)-catalyzed addition of o-halobenzoic acids to active internal alkynes (13JOC1660), rhodium(III)-mediated oxidative coupling ofbenzoic acids with disubsti-tuted alkynes (13T4454), palladium(II)-catalyzed tandem annulation reaction of o-alkynylbenzoates with methyl vinyl ketone (13T8626), and nickel(II)-promoted t-butyl isocyanide insertion in 2-(o-bromophenyl)-1-ethanones followed by hydrolysis (Scheme 69) (13SC3262). 

Miller KJ, Kitagawa TT, Abu-Omar MM (2001) Kinetics and mechanisms of methyl vinyl ketone hydroaDcoxylalion catalyzed by palladium(n) complexes. Organometallics 20 4403-4412... 

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