Vilsmeier-Haack-type reaction

Vilsmeier-Haack-type reaction provided the C ring of the Aspidosperma skeleton, and elaboration of the E ring was achieved by the addition of a radical generated from the xanthate derivative of the primary alcohol to give nonacyclic compound 111. The final steps for the completion of the total synthesis consisted of the formation of a lactone ring, which was achieved by oxidation of the tertiary amine with potassium ferricyanide,... 

Chloroformic acid ester Vilsmeier-Haack-type reaction Ethoxymethylene compds. 

The Vilsmeier-Haack type adduct, formed by the reaction of oxalyl chloride with DMF can be also be employed for the activation of carboxylic acids, as shown in Fig. 8 [200]. 

Gold has discovered an interesting reaction leading to a Vilsmeier-Haack-type complex. When cyanuric chloride (CLXXXVIII) is dissolved in N,N-dimethylformamide at 20°C reaction occurs with formation of the 1 2 complex CLXXXIX. If the reaction is conducted at slightly higher temperature an exothermic reaction occurs with evolution of carbon dioxide affording the iminium chloride CXC... 

The classical Vilsmeier-Haack reaction is one of the most useful general synthetic methods employed for the formylation of various electron rich aromatic, aliphatic and heteroaromatic substrates. However, the scope of the reaction is not restricted to aromatic formylation and the use of the Vilsmeier-Haack reagent provides a facile entry into a large number of heterocyclic systems. In 1978, the group of Meth-Cohn demonstrated a practically simple procedure in which acetanilide 3 (R = H) was efficiently converted into 2-chloro-3-quinolinecarboxaldehyde 4 (R = H) in 68% yield. This type of quinoline synthesis was termed the Vilsmeier Approach by Meth-Cohn. ... 

Another characteristic of electrophilic reactions of pseudoazulenes is the application of numerous cations as the electrophile, for example, diazonium salts and Vilsmeier- Haack s reagent (see Table VI), tropylium ion,135 triphenylmethyl cation,"4 pyrylium ion,119 and dithiolium ion.166 Very stable cations are formed (e.g., 120) addition of base releases the substituted pseudoazulene (see example in Eq. 10). Generally reactions of this type are thermodynamically favored (see also Section IV,B). The site of substitution... 

Well known compounds of this type are Vilsmeier-Haack adducts, imino esters, amidines, carboxylic orthoesters, orthoamides etc., which have proven their synthetic utility in thousands of reactions. As a consequence of the synthetic importance of these compounds, more or less extensive reviews are available for all of them. 

The benzocyclobutene-dihydroisoquinoline condensation shown in Scheme 12 gave the quaternary protoberberine salt (124 R = H), the intermediate dihydroderivative of this evidently losing hydrogen under the reaction conditions. " This type of salt [e.g. (124, R = OMe)] and its dehydro-analogue can be obtained by Vilsmeier-Haack reactions of 1-benzyl-3,4-dihydroisoquinolines and 1-... 

An earlier investigation (23) demonstrated that the Vilsmeier-Haack reaction of the ArCOCHj type compounds gives the monoformylated compounds or the corresponding P-chloro-vinyl aldehydes. It was found, however, that in the case of o-hydroxyacetophenones, the methyl group was doubly formyl-ated by a Vilsmeier reagent to give our first target compounds, 4-oxo-4H-l-benzopyran-3-carboxaldehydes ( ) in one step ( 1, J ). The reason why double formylation took... 

If the self-condensation of the iminium chlorides is minimized by suitable substitution, reaction with other reactive substrates is readily accomplished. Perhaps the best-known example of this type of reaction is the Vilsmeier-Haack aldehyde synthesis (121,285,286 general review of this reaction can be found in Houben-Weyl ( ). 

Two triphenylamino-substituted stilbene-type chromophores, with different electron acceptors, were synthesized via Vilsmeier-Haack reaction and Knoevenagel condensation [85]. These compounds can be easily incorporated into polymer backbone... 

Vilsmeier-Haack formylation of 2,5-diaryl-6a-thiathiophthens leads to the 3-formyl compounds, which are also obtainable from 3-aryl-l,2-dithiolium salts by treatment with triethylamine, and details have been given for the bromination of 2,5-disubstituted thiathiophthens. Nitration of 2-methylthio-5-phenyl-6a-thiathiophthen gives the 3-nitro-compound in poor yield, and attempted nitrosation experiments lead, in several examples, to rearranged structures of type (19), although the first stage of these reactions is presumed to be electrophilic attack on the 3-position. 

There are numerous multistep processes that generate electrophiles. As examples of these types of reactions, we will consider the diazotization of anilines and the formation of chloroiminium ions in the Vilsmeier-Haack reaction. Aryl diazonium ions are useful in the modification of arenes by the Sandmeyer reaction and as electrophilic intermediates in diazonium coupling reactions for the synthesis of dyes and pigments. Several types of synthetic methods have been developed for this chemistry, and the mechanism varies depending on the methodology [13]. Under some conditions, the nitrosonium ion (18) initiates the process (Scheme 1.5). NjOj and NOCl have also been proposed as intermediates in diazotization—both are considered as nitrosonium ion carriers. The aniline reacts... 

A novel synthesis of isoselenazoles (150), using bromoseleno-intermediates in the final cyclization stage, comprises the successive treatment, at -80 C, of selenoethers of type (148), e.g. cis-/3-methylseleno-2-propenal, with bromine and ammonia it generally affords the desired heterocycles in very good yield. The precursors (148) are ultimately derived from the appropriate ketones (146), which are first converted into the chloro-aldehydes (147) by the Vilsmeier-Haack reaction, and then treated with methaneselenol in pyridine-triethylamine. They arise as mixtures of cis- and trans-isomers, separable by spinning-band fractional distillation. The u.v. and n.m.r. spectra of the isoselenazoles were recorded and discussed. ... 

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