Vinylation, of ketones

Scheme 4.22 Vinylations of ketones with HOCSAC ligand.

Scheme 4.23 Alkylations, arylation and vinylation of ketones with transA, 2-diami-nocyclopentane-based ligand.

The a-arylation of carbonyl compounds (sometimes in enantioselective version) such as ketones,107-115 amides,114 115 lactones,116 azlactones,117 malonates,118 piperidinones,119,120 cyanoesters,121,122 nitriles,125,124 sul-fones, trimethylsilyl enolates, nitroalkanes, esters, amino acids, or acids has been reported using palladium catalysis. The asymmetric vinylation of ketone enolates has been developed with palladium complexes bearing electron-rich chiral monodentate ligands.155... 

Unsaturated Carbonyl Compounds 0-95 Vinylation of ketones or carboxylic esters... 

Buchwald has designed a hindered dialkylphosphino-binaphthyl ligand (3) that is much more active than the original ligand for asymmetric arylation of ketone enolates. Reactions occur at room temperature using only 2 mol % catalyst with enantioselectivities up to 94% [41]. Additionally, the Buchwald group has developed an electron-rich monodentate ligand (4) capable of vinylation of ketone enolates with up to 92% ee [42]. 

Catalytic asymmetric vinylation of ketones has been achieved. Vinylzinc reagents have been generated by hydrozirconation of terminal alkynes which are then transmet- allated with zinc.199 A titanium(IV) complex of a tims-cyclohexane-bis(sulfonamide) provides chiral catalysis it also facilitates dienylation of ketones, with ees also >90% in this case. 

Phenylseleno)acetaldehyde was recommended as an alternative synthetic equivalent to the vinyl carbocation for a-vinylation of ketones [30],... 

MAP-type ligands also catalyze asymmetric vinylation of ketone enolates (eq 11) with 56% ee for MAP (PPh2) and 90% ee for its PCy2 analogue (96% ee at —20°C). ... 

Metal-mediated additions of silyl enolates to alkynes also are valuable for intra-and intermolecular vinylation of ketones. The Hg(II)-induced cychzation of alky-nyl-branched SEE provides regio- and stereochemicaUy homogeneous exocychc vinyl mercurial products that can be converted into a variety of functionahzed alkenes [265-267]. Two plausible mechanisms for the intramolecular carbomercura-tion have been proposed, as in the above Pd(II)-mediated cycloaUcenylation-nu-cleophihc enolate addition to the Hg(II)-activated alkyne and concerted addition of an a-keto mercurial species generated by Si-Hg transmetalation. Forsyth et al. have determined that carbomercuration occurs in an anti fashion by the former... 

The a-vinylation of ketones by the use of organo-iron complexes has been extended to allow the introduction of an isopropenyl group (Scheme 38). The ethyl vinyl ether derivative has advantages over the methyl compound since the latter functions competitively as a methylating agent. 

A full paper describing the use of a-phenylselenoacetaldehyde in the a-vinylation of ketones has appeared (see Scheme 22). i8 The method may be extended to the introduction of isopropenyl groups. 

They are colourless liquids with characteristic odours, and are prepared by the condensation of ketones with alkyl orthoformates in the presence of alcohols, or by the reaction of acetylenes with alcohols in presence of HgO and BF3. In some cases trichloroethanoic acid is used as the catalyst. They lose alcohol when heated and form vinyl ethers. Exchange of alcohol groups occurs when the ketals of the lower alcohols are boiled with alcohols of greater molecular weight. See acetals. 

The interaction of (10) with vinylmagnesiiim chloride yields, after hydrolysis of the ketal group, 46% of the 3a-vinyl-l7-ketone (11b) and 7% of the 3j5-vinyl-17-ketone (12b). Ethynylation of (10) with potassium acetylide in dimethylformamide or with acetylene and potassium t-amyloxide in t-amyl alcohol-ether gives only the 3a-ethynyl derivative (11c) in 63% and 74% yields, respectively. ... 

Bohlmann (207) reported the reaction of /I -dehydroquinolizidine with methyl vinyl ketone and with propargyl aldehyde forming a partially saturated derivative of julolidine 135 and julolidine (136), respectively. Compound 135 can be prepared also by mercuric acetate dehydrogenation of ketone 137, which is formed by condensation of 1-bromoethylquinolizi-dine with ethyl acetoacetate (Scheme 11). 

Thermally reversible gels can be prepared from poly (vinyl alcohol) and alkali metal salts of o-hydroxybenzal derivatives having benzenoid groups at both ends 24). Colored gels can be obtained, depending on the type of ketone used (Figure 4). 

Ketones are generally not polymerizable, despite claims that acetone can be polymerized at low temperatures (1 ). A simple explanation for the lack of polymerizability of ketones compared to vinyl monomers can be deduced from consideration of Pauling (Z) average bond energies as shown in Equations 1 and 2, where AHP°l(est) is the estimated enthalpy of polymerization based upon the difference in bond energies of the two single bonds formed in the polymer compared to the double bond in the monomer ... 

The Nazarov cyclization of vinyl aryl ketones involves a disruption of the aromaticity, and therefore, the activation barrier is significantly higher than that of the divinyl ketones. Not surprisingly, the Lewis acid-catalyzed protocols [30] resulted only in decomposition to the enone derived from 46,47, and CO. Pleasingly, however, photolysis [31] readily delivered the desired annulation product 48 in 60 % yield. The photo-Nazarov cyclization reaction of aryl vinyl ketones was first reported by Smith and Agosta. Subsequent mechanistic studies by Leitich and Schaffner revealed the reaction mechanism to be a thermal electrocyclization induced by photolytic enone isomerization. The mildness of these reaction conditions and the selective activation of the enone functional group were key to the success of this reaction. 

Intramolecular hydrogen abstraction leading to the aziridine 344 has been proposed to account for the unexpected conversion of the /f-amino vinyl phenyl ketones 345 into the pyrroles 346.286... 

Bis(pyrazolyl)borate copper complex 47 has been employed as a catalyst in the homogeneous and heterogeneous styrene epoxidation reactions <00JCS(CC)1653>. Pyrazole palladacycles 48 have proven to be stable and efficient catalysts for Heck vinylations of aryl iodides <00JCS(CC)2053>. An asymmetric borane reduction of ketones catalyzed by N-hydroxyalkyl-/-menthopyrazoles has been reported <00JHC983>. 

In addition to alkoxides, carbonyl oxygens have occasionally been recruited to function as nucleophiles in allylic etherification processes. The cyclization reactions of ketones containing internal allylic systems occur through O-allylation under Pd catalysis to give rise to vinyl dihydrofurans203 or vinyl dihydropyrans (Equation (51))204,205 in good yields. 

Stoichiometric ionic hydrogenation of the C=C bond of a,/ -unsaturated ketones by HOTf and [Cp(CO)3WH] results in the formation of -ketone complexes of tungsten [32]. As exemplified in Eq. (17), hydrogenation of methyl vinyl ketone gives a 2-butanone complex of tungsten. The bound ketone is displaced by the triflate counterion, giving the free ketone. Similar reactions were reported for hydrogenation of the C=C bond of a,/ -unsaturated aldehydes. 

The third procedure illustrated by this preparation involves the reaotion of ketones with trifluoromethanesulfonic anhydride in a solvent such as pentane, methylene chloride, or carbon tetrachloride and in the presence of a base such as pyridine, lutidine, or anhydrous sodium carbonate.7-11,15 This procedure, which presumably involves either acid-catalyzed or base-catalyzed enolization of the ketone followed by acylation of the enol with the acid anhydride, has also been used to prepare other vinyl sulfonate esters such as tosylates12 or methanesulfonates.13... 

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