Methyl vinyl ketone, reaction with

Similar cycloaddition reactions were observed with methyl vinyl sulfone (48) and )3-nitrostyrene (48,51). Methyl vinyl ketone, on the other hand, is reported to give dihydropyrans as the initial products (50,52,53). Thus (16) on reaction with methyl vinyl ketone at room temperature for 12 hr gave a 60% yield of 2-dimethylamino-3,3,6-trimethyl-3,4-dihydro-2H-pyran (59). 

The second group of reactions is called vicinal difunctionalization. They embrace the C2 and C3 positions of the furan ring simultaneously. Thus, complex 3 (X = O, R = R = R = H) reacts with benzaldehyde dimethyl acetal to give 4H-furanium cation (the product of electrophile addition at C4), which experiences further attack by the methoxide group with formation of the acetal 8 (950M2861). This reaction is possible in the presence of the Lewis acid (BF3—OEt2). Reaction with methyl vinyl ketone in methanol, when run in identical conditions. 

Another example in which A-methyl-l,2-dihydropyridine (41a) behaves as an enamine rather than a diene is its reaction with methyl vinyl ketone (44) (64JCS2165). The product is a pyran 45, which is obtained in 100% yield, rather than an isoquinuclidine derivative (80JOC1657). 

Morpholmo-l cyclohexene, reaction with methyl vinyl ketone, 46, 80... 

Reactions of furan (5) under solvent-free conditions, catalyzed by Montmorillonite K10, have been described by Cintas [27]. The reaction with methyl vinyl ketone (32) produced Michael addition in positions 2 and 5, whereas reaction with symmetrically substituted cyclic dienophiles produced a mixture of the endo and exo adducts with the kinetically favored endo adduct predominating, except when maleic anhydride (39) was used as the dienophile (Scheme 9.2). 

In the case of the electron poor alkenes, results were more varied. Under all conditions examined, reactions with methyl vinyl ketone, acrylonitrile, methacrylonitrile and 4-vinyl pyridine afforded products with IR spectra equivalent to those obtained without the addition of the alkene (side reaction). In the cases of vinyl bromide and chloromethyl styrene, unreacted PCTFE was recovered unchanged. It is speculated that electron transfer to the alkene proceeded in each case. While the product of vinyl bromide reduction was not observed, perhaps because of volatility, one could isolate poly(chloromethylstyrene) in the latter case. 

Linders, J.T.M., Briel, P., Fog, E., Lie, T.S. and Maat, L., Chemistry of opium alkaloids, Part XXVIII preparation of 6-demethoxy-N-formyl-N-northebaine and its Diels-Alder reactions with methyl vinyl ketone and nitroethene novel 8-nitro-substituted 6a,14a-ethenoisomorphinans and 6 3,14 3-ethenomorphinans, Rec. 

Most recently, B-halo-l-alkenyl-9-BBN s have revealed to undergo a 1,4-addition reaction to ae,P-unsaturated ketones such as methyl vinyl ketone. Hydrolysis of the initially formed intermediates produces the corresponding (Z)-5-halo-y,5-unsaturated ketones in good yields stereospecifically (>98%),88). In the reaction with methyl vinyl ketone, the major products isolated after hydrolysis are not the expected halo-enones but the aldol adducts, which are readily converted into the halo-enones by treatment with sodium hydroxide, as depicted in Scheme 3. No aldol adducts are formed in the case of enones other than methyl vinyl ketone. 

Annelation of steroidal dienamines with substituted phenacyl bromides (7 examples) or with benzenediazonium salts (11 examples) has been shown to lead to the corresponding furano- and indolo-steroids.89 Thus the A3,5-dienamine derived from A4-androstene-3,17-dione reacted with p-bromophenacyl bromide to yield the A5-androstano[3,4-h]furan (199) in 26% yield, and reaction of the same A3,5-dienamine with benzenediazonium fluoroborate at -45 °C led to formation of the hydrazone (200) which underwent Fischer-indole cyclization on treatment with phosphorus oxychloride to produce the A4-androstano[6,7-6]indole (201). The A3,5-dienamine derived from 17/3-acetoxyandrost-4-en-3-one has been converted into the benz[4,5,6]-steroid (202 R1 = Me, R2 = H) by reaction with methyl vinyl ketone and into the analogous benzsteroid (202 R1 = H, R2 = Me) on treatment with crotonal-dehyde.90 A route to the condensed pyrroline ring system (203) has been devised... 

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. 

Saccharin 1 adds on to activated double bonds. In a base-catalyzed reaction with methyl vinyl ketone, N-(3-ketobutyl)saccharin150 is formed. Acid catalyzed addition of 1 to 2,3-dihydropyran occurs as expected, again at the nitrogen,151,152... 

Since both oxidative splitting of the double bond and aldol condensation represent reliable and general reactions, their sequence serves as an efficient route for the transformation of readily available cyclohexene systems e.g. formed via the Diels-Alder reaction or Robinson annulation) into functionalized cyclopentene derivatives. This standard operational mode is extensively used in total syntheses. One of the numerous examples, the synthesis of helminthosporal 463, the sesquiterpenoid toxin of fungi, is shown in Scheme 2.150. In the initial phases of the synthesis, commercially available (—)-carvomenthone 464 was transformed into 465 via Michael reaction with methyl vinyl ketone to give 466 and subsequent intramolecular aldol condensation. 

However, the maximum level of stereochemical control in these processes with a variety of electrophiles (CH =CHC02Me, CH2—CHCN, BrCH2CH=CH2, BrCH2C02Et) was below 60% optical purity (corresponding to a ratio no better than 4 1). These results appear to be the result of kinetic control in the transition state for carbon-carbon bond formation. On the other hand, reactions with methyl vinyl ketone can be run under either kinetic or thermodynamic control and the level of stereochemical control is higher under the conditions. - Likewise, the enamine from 2-methoxymethylpyrrolidine... 

The fused salt CsOH-CsF acts as a desilylating reagent on ketene silyl acetals to give the equivalent enolate. The reaction proceeds at -60 °C. The equivalent reaction with methyl vinyl ketone proceeds by 1,4-addition (Scheme 2.32) [22]. 

Treatment of 4-(l-aryl-l-hydroxymethyl)-2,2-dimethylchromenes with PBrs at 0 °C produces the 4-arylidenechroman e.g. 13 <05TL8849>. The cannabinoid ring system has been obtained from 27f-[l]benzopyran-3-carboxaldehydes by conversion to the 3-vinyl derivative and a subsequent thermal DA reaction with methyl vinyl ketone <0581888>. 

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