Vinylogous acyl chlorides

D. Diirr139 has described attempts to obtain derivatives of the 1,3-dithiepinyl cation (213) (which is a vinylog of 205) by condensing biphenyl-2,2 -dithiol with aldehydes or acyl chlorides under the conditions proposed by Wizinger and Soder.5 These attempts, however, were completely unsuccessful. If we accept these results as sufficient evidence of the instability of the cation, this instability can be explained by the fact that the seven-membered ring containing... 

The catalytic cycle of this NHC-catalyzed reaction originates by the addition of the NHC to the vinylketene 39, which in turn was created from the acyl chloride 43 in basic media, to afford the diene A as an intermediate (Scheme 17). The diene A and ketone 47 are subjected to hetero—Diels—Alder (HDA) cycloaddition reaction or undergoes a stepwise vinylogous aldol reaction with intramolecular cyclization to afford the zwitterionic B. The breakdown of zwitterionic B gives the dihydropyra-none 48 and recreates the NHC catalyst (Scheme 17) (2011MI1943). 

Dicarboxylic acid dichlorides with less than seven carbon atoms do not react to give tetraketones similar to 117, but instead undergo an intramolecular acylation (72) to give on hydrolysis the vinylogous acid anhydride (118), e.g., from succinyl chloride and the enamine (113). 

Acylation of the vinylogous pyrrolidine amide of dimedone with acetic anhydride or acetyl chloride led (possibly indirectly) to the carbon acylation product, whereas trichloroacetyl chloride gave rise to products derived from attack of chloride at the oxygenated double bond position in an initial 0-acylation product (401-404). 

The acylation of enamines derived from cyclic ketones, which can lead to the acyl ketone or ring expansion (692-694), was studied by NMR and mass spectroscopic analysis of the products (695,696). In a comparative study of the rates of diphenylketene addition to olefins, a pronounced activation was observed in enamines (697). Enamine N- and C-acylation products were obtained from reactions of Schiff s bases (698), vinylogous urethanes (699), cyanamides (699), amides (670,700), and 2-benzylidene-3-methylbenzothiazoline (672) with acid chlorides, anhydrides, and dithio-esters (699). 

The intermediacy of ketenes in some enamine acylation reactions using acid chlorides was described above (386,387). Direct addition of ketene to enamines was studied simultaneously by several groups (414-420). The initially formed aminocyclobutanone products could be isolated in some instances, depending on the substitution of the initial enamine. Opening to give either the acylated enamine or the alternative vinylogous amide was found to occur spontaneously or on heating, particularly in adducts derived from enamines with an olefinic proton. 

Photochemical equilibration of the 3 2 stereoisomeric mixture of N-acyl vinylogous ureas in DMF by irradiation at 300 nm in a Ray-onet reactor equipped with a stannous chloride filter solution at 37 °C for 4 h leads to a 6 1 mixture of trans-Aa b and c .v-Aa b paly-toxins. The total synthesis of palytoxin (1) is now complete. 

Methyl-1,2-dihydroisoquinoline has been reacted8,66 with a variety of acid chlorides (Table III) the expected vinylogous amides (64) were isolated in most cases. 2-Benzyl-l,2-dihydroisoquinoline behaves similarly. The acylation reaction fails with simple aliphatic acid chlorides. Sometimes, the reaction of the enamine with the acid in the presence of dicyclohexylcarbodimide succeeds. The 1,2-dihydro-isoquinoline (65) also reacts with ethoxalyl chloride to yield 66.86... 

The photochemistry of 2-acyl-vinylogous amides has also been investigated by Tamura and coworkers, who reported that irradiation of 142 (R1 = CH2R R2 = H R1 = R2 = CH2R) through a quartz filter in methylene chloride led to the formation of the dealkylated product 143, albeit in modest yield (equation 19), both in the case of... 

Vinylogous a-diazoketones from vinylogous carboxylic acid chlorides— 4-Acyl-5-diazomelhylisoxazoles, condensed isoxazoles s. 17, 854... 

Hydrolysis of Vinylogous Thioacetals. Carbanions prepared by lithiation of y-phenylthioallyl phenyl thioethers can serve as synthetic equivalents of /3-acyl vinyl anions. Umpolung of the usual electrophilic reactivity of 2-cyclohexenone is achieved by a sequence exploiting electrophilic capture of a hthiated vinylogous thioacetal and subsequent CuOTf-assisted hydrolysis (eq 57). Otherwise unfunctionalized vinylogous thioacetals can be hydrolyzed to enones by mercury(II) chloride in wet acetonitrile. However, the keto-substituted derivative in eq 57 gave only a 25% yield of enone by this method. A superior yield was obtained by CuOTf-assisted hydrolysis. ... 

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