Subject Vilsmeier reaction

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When (190) was subjected to a Friedel-Crafts reaction with benzoyl chloride, the result was an analog of coralyne with a phenyl rather than a methyl group at position 8. Kametani et al. (74YZ478) have carried out a parallel study using the Vilsmeier-Haack reaction to produce norcoralyne. 

Both thienothiophenes (3) and (7) were subjected to competitive electrophilic substitution reactions with thiophene. The fused heterocycles were always more reactive than thiophene in acetylation, Vilsmeier formylation and chlorination with NCS. While acetylation of both (3) and (7) occurrred at a comparable rate, formylation and chlorination occurred faster in the [3,2-6]-fused isomer (3) than in the [2,3-6] isomer (7). 

A 4-bond synthesis of pyridines from carbonyl compounds, which were subjected to Vilsmeier-Haack conditions giving the conjugated iminium salts, has been achieved by reaction with ammonium acetate (Scheme 113)... 

We include in this section formylation reactions involving carbon monoxide, hydrogen cyanide, formyl fluoride and dichloromethyl alkyl ethers." The Vilsmeier and Reimer-Tiemann formylation reactions are the subjects of other chapters (Volume 2, Chapters 3.4 and 3.5). 

Asokan et al. has developed a practical synthesis of 4-chloropyridines 1 from carbonyl compounds having two enolizable carbons adjacent to the carbonyl such as compound 2 <04T5069>. Ketone 2 was subjected to Vilsmeier-Haack reaction conditions leading to the... 

Vilsmeier formylation of 2-benzylisoindole gives the 1-formyl derivative (61%).25 With 1-phenylisoindole reaction occurs at the unsubstituted a-position the intermediate iminium salt on neutralization gives the cross-conjugated enamine system 78, which has been isolated and characterized. X-Ray analysis confirms the assigned structure.95 On hydrolysis, the formyl derivative, which has also been the subject of X-ray crystal analysis (Figs. 4 and 5), is formed. As expected from the analogy with pyrrole chemistry, the aldehyde does not readily form typical carbonyl derivatives. 

Subjecting acetanilides to the conditions of the Vilsmeier-Haack reactions is an effective method for the preparation of quinolines <8iJCS(Pi)i537>. On the other hand, if the phenacetanilide of anthranilic acid is subjected to the identical reaction conditions, 4-dimethylamino-3-phenyl-5H-benz[()]azepine-2,5-dione (189) is formed in high yield <84S349>. The phenyl group of anthranilic acid may be replaced by thienyl and pyridyl without loss in the efficiency of cyclization. 

The above route also proved to be economically less viable, therefore, we decided to use the commercially available p-amino phenol to carry out a similar set of reactions. p-Amino phenol was condensed with dimethoxy tetrahydrofuran to obtain the i -aryl pynole 41. The phenol 42 was converted to the acetate and that was subjected to die Vilsmeier/Friedel-Crafts acylation conditions to obtain the aldehyde 43. Decarbonylation of the aldehyde followed by Wolff-Kishner reduction and esterification resulted in the formation of con imd 45. Similar results were obtained starting with p-anisidine. In this case demethylation was carried out using boron tribromide. The phenolic group... 

Benzo-l,4-thiazines and Related Compounds.— The chemical behaviour of the Vilsmeier product (111), derived from l,4-benzothiazin-3(4H)-one, has been the subject of detailed studies. Hydrolysis under different conditions affords the acid (112), the aldehyde (114), or the chloro-aldehyde (113), depending on the method of hydrolysis. Treatment of the perchlorate of (111) with DMSO leads to the displacement of the chlorine atom to give the dimethylsulphoxonium derivative (115), while reaction with pyridine proceeds with selective attack at the aminomethylene function, yielding the pyridinium salt (116). This latter reacts readily with aniline in acetic acid medium to give, along with 2-formyl-3-anilino-l,4-benzothiazine (117), the anilinomethylene derivative (120), whose formation probably involves an intramolecular rearrangement of the intermediate pyridinium salt (118), as depicted. 

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