Vinylogs syntheses with

The condensation of a vinylogous formamide with an enamine has been applied to an aza azulene synthesis (351). The point of attachment of the aldehyde to the enamine in condensations with indolenin derived poly-enamines was found to favor the second double bond (352,353). 

McKinnon and Buchschriber used 1,2-dithiol-3-thiones (9) and substituted acetylenedicarboxylates in the synthesis of thioaldehydes in which the thioformyl group is in vinylogous conjugation with a sulfur heterocycle (71CJC3299). These thioaldehydes (10) can be described as the structure 10b, but X-ray results show that structure 10a is a more correct representation [74ACS(B)964 75BSF1435]. 

Yet another development which is worth mentioning in this context is the 5n substitution of acetals of unsaturated carbonyl compounds. The phenomenon that the reaction of an allylic acetal with a Grignard reagent in the presence of CuBr may occur as a vinylogous substitution with double bond shift has been long known.The reaction can be utilized in an efficient synthesis of 3-substituted propionaldehydes using the acrolein acetal as a homoenolate cation equivalent (Scheme 38). ... 

Edmondson, S.D., Mastracchio, A. and Parmee, E.R. (2000) Palladium-catalyzed coupling of vinylogous amides with aryl halides applications to the synthesis of heterocycles. Org. Lett., 2, 1109-12. 

A related enamine alkylation is seen in the rearrangement of an ethylene imine vinylogous amide, which was heated with sodium iodide in diglyme. The presumed internal enamine alkylation constitutes a critical step in an oxocrinane synthesis (265). Use of an ethylene imine urethane for alkylation of an enamine and formation of the hexahydroindole system has also been reported (266). 

Alkylation of enamines with epoxides or acetoxybromoalkanes provided intermediates for cyclic enol ethers (668) and branched chain sugars were obtained by enamine alkylation (669). Sodium enolates of vinylogous amides underwent carbon and nitrogen methylation (570), while vicinal endiamines formed bis-quaternary amonium salts (647). Reactions of enamines with a cyclopropenyl cation gave alkylated imonium products (57/), and 2-benzylidene-3-methylbenzothiazoline was shown to undergo enamine alkylation and acylation (572). A cyclic enamine was alkylated with methylbromoacetate and the product reduced with sodium borohydride to the key intermediate in a synthesis of the quebrachamine skeleton (57i). 

An interesting synthesis of quinolizidines was achieved using a vinylogous variation of the Bischler-Napieralski reaction. Angelastro and coworkers reported that treatment of amide 26 with PPSE (polyphosphoric acid trimethylsilyl ester) followed by reductive... 

Having retraced the remarkably efficient sequences of reactions which led to syntheses of key intermediates 14 and 15, we are now in a position to address their union and the completion of the synthesis of the spiroketal subunit (Scheme 6b). Regiocontrolled deprotonation of hydrazone 14 with lithium diisopropylamide (LDA), prepared from diisopropylamine and halide-free methyl-lithium in ether, furnishes a metalloenamine which undergoes smooth acylation when treated with A-methoxy-A-methylcarboxa-mide 15 to give the desired vinylogous amide 13 in 90% yield. It is instructive to take note of the spatial relationship between the... 

Although a number of reagents can be used to reduce an isoxazole ring, molybdenum hexacarbonyl31 was selected for use in this synthesis. The action of this reagent on 24 reduces the weak N-0 bond of the isoxazole ring and produces a //-amino-a,//-unsaturated aldehyde (i.e. a vinylogous formamide) (see Scheme 19). Intermediate 87 forms smoothly upon deprotection of the terminal acetylene carbon with basic methanol-THF. 

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. 

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