Vilsmeier conditions, cyclization under

Thermal cyclization of l-(l-methyl-2-pyrrolyl)buta-l,3-diene yields l-methyl-4,5-dihy-droindole (77TL151) and several examples of the cyclization of substituted vinyl derivatives have been reported, e.g. (395) -> (396) <74JCS(Pl)153l), (397) -> (398) <80JCR(S)233>, whilst the 2-(2-indolyl)propenoic ester (399) cyclizes under Vilsmeier-Haack conditions to produce (400) (80T2125). 

Interestingly, o-cyanomethoxybenzonitrile (26) gives a Thorpe-Ziegler type of cyclization under Vilsmeier conditions (DMF/POCl3), that is without the addition of a base. Further cyclization of the assumed 3-amino-2-cyanobenzofuran 27 with the Vilsmeier reagent afforded benzofuro-[3,2-d]pyrimidine (28) in poor yield, (91JHC263) (Scheme 7). 

Furo[3,2-fa]benzothiophenes (37) were synthesized in an analogous way (91JHC269) by smooth cyclization of the cyanomethyl ether 36 in the presence of K2C03/DMF. The starting 2-cyano-3-hydroxybenzothiophene 35 was obtained from methyl 2-thiohydroxybenzoate and chloroacetonitrile. Under Vilsmeier conditions (POCl3/DMF), the 2-cyano-3-cyanomethoxy-... 

Cyclic enamines and imines, 6, 147 Cyclic hydroxamic acids, 10, 199 Cyclic peroxides. 8, 165 Cyclizations under Vilsmeier Conditions, 31, 207... 

An unprecedented attack on an azide group by an iminium species, generated in situ under Vilsmeier conditions, furnishes a novel route to construct the imidazole ring. Thus, A -aryl-5-chloro-2-(dimethylamino)imidazole-4-carbox-aldehydes 1257 were obtained from the Vilsmeier cyclization of A -aryl-2-azidoacetamides 1256. The possible mechanism for the reaction is illustrated in Scheme 316 <1998JOC7136>. 

Meth-Cohn, O., Tamowski, B. Cyclizations under Vilsmeier conditions./Adv. Heterocycl. Chem. 1982,31,207-236. 

Pyrrole reacts with malonamides in phosphoryl chloride giving pyrroli-zines in moderate yields (Scheme 6).15 Benzimidazole-2-propionic acid undergoes cyclization and subsequent formylation under Vilsmeier conditions at room temperature (RT) (Scheme 7).16... 

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