Primary Vilsmeier-Haack reaction

A rare example of the Vilsmeier- Haack reaction succeeding with a primary amine is provided by 4-amino-3-methyltriazole (33), which, when heated... 

As primary step, a (formal) vinyl substitution of chlorine in 24 takes place consisting of Michael addition of thiolate and concomitant elimination of HCI. The intermediate 25 cyclizes by intramolecular aldol condensation to give 26. P-Chlorovinyl aldehydes (24) are prepared from a-methylene ketones by reaction with DMF/POCI3 (Vilsmeier-Haack reaction). 

The formylation of 2-methylbenzothiazole by the Vilsmeier-Haack reaction using dimethylchloroformiminium chloride (82) in DMF yields the l,3-bis-dimethylamino-2-(2-benzothiazolyl)propenium salt (83), which is hydrolysed by alkali to 2-benzothiazolylmalonic dialdehyde (84). The corresponding quaternary salt (85) reacts similarly in DMF, yielding (86) as the final product. In chloroform, however, its formylation followed by hydrolysis affords the trimethine dyes (87 R = H or CHO) and (88). Their formation is ascribed to the condensation of the primary formylation products with an excess of quaternary salt. A series of reactions based on 3-methylbenzoselenazole take an entirely parallel course. ... 

Reaction of A -acylamino acids with the Vilsmeier-Haack reagent leads to 2-alkyl-4-[(Af,Af-dimethylamino)methylene]-5(47i)-oxazolones 814. The reactivity of these compounds with various nucleophiles has been studied. Primary alkylamines undergo amine exchange with 814 to afford 2-alkyl-4-[(alkylamino)methylene]-5(4/i)-oxazolones 815 (Scheme 7.250). ° ... 

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,... 

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