Cross with vinyl ketone

In the Mukaiyama aldol additions of trimethyl-(l-phenyl-propenyloxy)-silane to give benzaldehyde and cinnamaldehyde catalyzed by 7 mol% supported scandium catalyst, a 1 1 mixture of diastereomers was obtained. Again, the dendritic catalyst could be recycled easily without any loss in performance. The scandium cross-linked dendritic material appeared to be an efficient catalyst for the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene. The Diels-Alder adduct was formed in dichloromethane at 0°C in 79% yield with an endo/exo ratio of 85 15. The material was also used as a Friedel-Crafts acylation catalyst (contain-ing7mol% scandium) for the formation of / -methoxyacetophenone (in a 73% yield) from anisole, acetic acid anhydride, and lithium perchlorate at 50°C in nitromethane. 

Alkyl halides possessing / -hydrogens are usually poor substrates for carbonylative cross-coupling due to competitive / -hydride elimination/ Allyl chlorides can be used in carbonylative cross-coupling with allylstannanes/ phenyl-, 3-furyl, or vinylstannanes " to afford allylketones in modest to good yields. Divinylketones can be accessed through the reaction of vinylstannanes with vinyl iodides or vinyl triflates, with the latter requiring the addition of LiCl. Synthetic potential of this method has been proved in the formation of macrocyclic ketone jatrophone. In the reaction of vinyl triflates with tetramethyltin or aryltrimethylstannanes the additional activation by ZnCle is required. 

An example prepared by tin-lithium transmetallation is compound 637, which reacts with enolizable ketones, after transmetallation with cerium(III) chloride895. This intermediate was transformed into the corresponding vinylzinc reagent and, after palladium(O)-catalyzed cross-coupling reactions with aryl iodides, was used in the synthesis of the antitumor antibiotic rineomycinone B2 methyl ester940,941. The vinyllithium 627 has also been transformed into the corresponding vinyl iodide by stannylation followed by reaction with iodine. The arylation has been performed in this case by a palladium(0)-catalyzed... 

Octalone dienamines, e.g. 152, have shown a remarkable solvent dependence in the reaction with methyl vinyl ketone (equation 31)86. In methanol, reaction occurs primarily at the less reactive -position of the dienamine and the mechanism probably involves a prototropic shift in the initially formed enolate anion to give 153, and subsequent cyclization onto C-8a of the enimmonium salt to give 154. In toluene, the change in regioselectivity is complete and the product obtained is 157, which must arise from 156, formed in turn from cycloaddition to cross-conjugated dienamine 155. 

A change in the course of the reaction of methyl vinyl ketone with A1,8fl-2-octalones was observed38,39 when a carbonyl group was introduced at C-5. In this case no y,(5-annulation occurred but, in addition to [4 + 2] cycloaddition to the cross-conjugated... 

Cross aldol reaction between two different aldehydes and/or ketones without prior activation or protection should provide a straightforward methodology for the synthesis of aldols, Mahrwald recently reported that treatment of aldehydes with TiCU and NEta (or TMEDA) gives rise to syn- do reaction in good yields (Eqs 38 and 39) [141], This method was extended to the aldehyde-ketone cross aldol reaction catalyzed by TiCU [142], an advantage of which is that reaction occurs at the more encumbered a-position of unsymmetrical ketones, as illustrated in Eqs (40) and (41) [143], The use of aliphatic aldehydes instead of PhCHO usually reduced stereoselectivity. When TiCU was replaced by a catalytic amount of BuTi(0-/-Pr)4Li, the aldol reaction was followed by the Tischenko reaction [144], Methyl vinyl ketone trimerized to give a chlorinated cyclic product with TiCU [145],... 

Acid hahdes can also be used in Migita-Kosugi-Stille coupling in this C-C bond formation fhe corresponding ketone is produced. Subjection of a benzoyl chloride derivative prepared in situ to cross-couphng with a vinylstannane provided the desired vinyl ketone which was successfully transformed to a potent COX-2 inhibitor (Scheme 12.99) [201],... 

The 1,2-thiaphospholes (20) react thermally with norbornadiene, norbornene, or diethyl azo-dicarboxylate to produce double Diels Alder cycloadducts (24) and (25). With mixtures of norbornadiene and methyl acrylate or acrylonitrile, crossed double Diels-Alder cycloadducts are obtained. In the presence of AICI3 the 1,2-thiaphospholes (20) react with acrylic esters, acrylonitrile or methyl vinyl ketone to give tandem Diels-Alder/Michael adducts such as (26). The AICI3-promoted reaction of (20) with ethyl propiolate affords with the elimination of a sulfur atom the stable phosphinine (27) (Scheme 4) <94BCJ2785>. 

A triflyloxy substituent may replace the iodo substituent in an efficient approach to carbon-carbon bond formation in alkenes and arenes. Applied to pyrimidine chemistry, it has been found that cross-coupling of 5-triilyloxyuracil with alkenes and alkynes leads to 5-alkenylated and 5-alkynylated uracils (87H355). Similarly M-methyl- or Af,N -dimethyl-pyrimidin-5-yl triflate (16) reacts with styrene, acetonitrile, methyl acrylate, or methyl vinyl ketone to form the alkenylated products (17) (87H355). 

Siloxane-based sealants cure either by condensation or addition reactions (22). One-package systems are available that cure in the presence of atmospheric moisture. The cross-linking reaction results in the elimination of either acetic acid or methyl ethyl ketone depending on the resin system. The more conventional two-package systems use metallic soaps such as dibutyl tin dilaurate to catalyze the cross-linking with the subsequent elimination of ethyl alcohol. Addition cures can also be accomplished with vinyl-containing polysiloxanes and a transition metal catalyst. 

As shown in Table 11, the photoreduction process is quite efficient in phenyl vinyl ketone copolymers with styrene. Because of the rapid intersystem crossing in the phenyl ketone chromophore, it seems likely that both the reduction and chain scission processes proceed via the intermediacy of the triplet state. 

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