Methyl vinyl ketone conformation

The case of a, -unsaturated caAonyl compounds is analogous to that of 1,3-dienes, in that stereoelectronic factors favor coplanaiity of the C=C—C=0 system. The rotamers that are important are the s-trans and s-cis conformations. Microwave data indicate that the s-trans form is the only conformation present in detectable amounts in acrolein (2-propenal). The equilibrium distribution of s-trans and s-cis conformations of a,fi-unsatuiated ketones depends on the extent of van der Waals interaction between substituents. Methyl vinyl ketone has minimal unfavorable van der Waals repulsions between substituents and exists predominantly as the s-trans conformer ... 

If the vinylallene possesses a substituent at the vinylic terminal position, an endo adduct is preferentially obtained owing to the secondary orbital overlap. Only the E-isomer of propenylallene underwent the regio- and stereoselective cycloaddition with methyl vinyl ketone to afford the endo-isomer as the major product. The Z-iso-mer was unreactive because it preferred the transoid conformation [165]. 

Microwave-assisted Diels-Alder reactions of 9-substituted anthracenes with 2-acetamidoacrylate in DMF generate conformationally constrained bicyclic bisaryl a-amino acid derivatives with high regioselectivity.138 The Sc(OTf)3-catalysed Diels-Alder reaction of anthracenes with methyl vinyl ketone does not proceed via an electron-transfer process from anthracenes to the MVK-Sc(OTf)3 complex.139 (-)-(/ )-9-(l,2-Dimethoxyethyl)anthracene has been used as a chiral template in the Diels-Alder/retro-Diels-Alder sequence for the synthesis of a,j3-unsaturated lactams.140... 

Durig and Little (1981) determined the conformational barriers to internal rotation of methyl vinyl ketone by IR and Raman spectroscopy. They recorded IR spectra of the gaseous and the solid states and the Raman spectrum of the liquid state. They also determined the potential function for internal rotation of the asymmetric top and obtained the following potential constants VI = 180 9, V2 = 827 107, V 3 = 113 8, and V4 = 150 34 cm. According to these data, the s-trans conformer is the predominant form at ambient temperature, and the enthalpy difference between the s-trans and the s-cis conformer in the gas phase is 280 cm. The relative intensities of the Raman bands as a function of the temperature afford an enthalpy difference of 172 cm for the liquid. 

The reaction of endocyclic enamines with a,p-unsaturated ketones to afford cu-fused hydroindolones or hydroquinolones constitutes a complementary and highly useful annulation sequence developed extensively by Stevens and coworicers, see the reaction of (5) to give (6) in Scheme 7. ° The importance of stereoelectronic effects is highlighted in the reaction of (7) with methyl vinyl ketone, which provided only the alkylated product (8) and none of the expected ci5-hydroindolone (9)." The failure of intermediate (8) to cyclize in this case was attributed to nonbonded interactions between the aryl group and the side chain. This destabilizing allylic interaction s disfavors formation of conformer (10), the intermediate required for antiperiplanar addition of the enol nucleophile (Scheme 8). Cyclization via the alternate conformation would require a double boat-like transition state. 

The equilibrium distribution of s-trans and s-cis conformations of substimted a,6-unsaturated ketones depends on the extent of van der Waals interaction between the C(l) and the C(4) substituents.Methyl vinyl ketone has the minimal unfavorable van der Waals repulsions and exists predominantly as the s-trans conformer. 

The conformation of 5,6-dihydro4//-l,3-selenadiazine 39 has been described (see Section 9.15.4). This selenadia-zine can be converted to the 6/7-1,3-selenazine 149 by treatment with methyl vinyl ketone at elevated temperature (Scheme 38) <1998T2545>. The AT-selenoacylamidine 148 is an intermediate in this reaction (see following section). 

Kappe and co-workers employed an isomunchnone generation-trapping sequence to access conformationally restricted dihydropyrimidine derivatives as novel calcium channel modulators. The stable isomunchnone 481 was prepared from dihydropyrimidone 479 by the standard A -malonylacylation and azide transfer to give 480, and then treatment of the latter with rhodium acetate (Scheme 4.19). Isomunchnone 481, which is stable in the open air for months, reacts with N-methylmaleimide and methyl vinyl ketone to give adducts 482 and 483, respectively, the latter arising by rearrangement of the primary adduct. 

Suter has described the considerations which apply to the development from the conformational analysis of small molecules of a semiempirical force field for a new type of polymer structural unit." The force field thus chosen was based upon aldehydes and ketones, and was ultimately applied to poly(methyl vinyl ketone). 

B-l-Alkynyl-9-BBN, easily and quantitatively prepared by the reaction of boron trifluoride-diethyletherate with the corresponding lithium methyl alkynyldial-kylborinate [12], undergoes a smooth 1,4-addition in pentane at room temperature to methyl vinyl ketone (MVK) and ketones capable of adopting cisoid conformation [13]. The reaction proceeds through srx-membered cyclic transition state to afford the enol borinate intermediate, which on hydrolysis afford y,6-acetylenic ketones, in high yields (Scheme 7.8). 

In most aj3-unsaturated ketones two conformations are possible and two carbonyl bands can be seen. These often differ very widely in intensity. The two bands correspond to 5 cis and s trans forms, although it is not uncommon for the s cis form to be replaced by a skew configuration. Barlet et al. [99] have described a method for the determination of the configuration of unsaturated ketones. Typical values for methyl vinyl ketone are 1716 and 1686 cm , and for ethyl vinyl ketone [98] 1707 and 1690 cm. In all cases it is assumed that the lower frequency band is derived from the trans form in which the delocaUsation is expected to be the greater. In a few instances steric hindrance allows only one form, as in CH3CH=C(CH3)2 which has only one band at 1693 cm". ... 

Its formation is favoured over other cyclic conformations by entropy considerations. In solid polymers where certain conformations are more favoured than others, entropy considerations might be less important. It has been shown that the Norrish Type II reaction in poly(phenyl vinyl ketone) occurs via a six-membered cyclic intermediate [510], whereas in poly(methyl methacrylate —CO— methyl vinyl ketone) it occurs via a seven-membered transition state [122]. 

Ghosh AC, Portlock DE, DalzeU HC, Malberg C, Herligy P, Razdan RK (1983) Diels-Alder reaction of fi-dihydrothebaine and its 4-phenyl ether with methyl vinyl ketone synthesis of 6,14-exoethenomorphinans. J Org Chem 48 4137-4139 Glasel JA (1981) A comparison of solution solid state and theoretical conformations of morphine. Biochem Biophys Res Commun 102 703-709 Gordon M (1974) Annu Rep Med Chem 9 38-50... 

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