Esters Vilsmeier reagent

Amino groups react very easily with aldehydes or ketones, and with aldehydes in the presence of amines, they can be acylated by the usual acylating agents, and they react with amidacetals, Vilsmeier reagents and nitroso compounds (Scheme 12). As mentioned earlier, alkylation leads mainly to AT(2)-alkylated products. The hydrazino group reacts in the same way as the amino group with aldehydes or ketones, with acyl chlorides or carboxylic anhydrides, with sulfonyl chlorides, ortho esters, carbon disulfide and with nitrous acid. The last three reactions have mainly been used for the synthesis of condensed 1,2,4-triazines. 

RCOOH — RCHO. The iminium salt (1) formed on reaction of a carboxylic acid with the Vilsmeier reagent (formed from DMF and oxalyl chloride) is reduced by lithium tri-/-butoxyaluminum hydride (1 equiv.) to an aldehyde. The chemo-selectivity is noteworthy ester, nitrile, keto, and halide groups are not affected.3... 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

Ethoxycarbonylmethyl-3-pyridinecarboxylic acid (99) with a Vilsmeier reagent (made in situ) gave 6-methyl-5-oxo-5,6-dihydro-1,6-naphthyridine-8-carboxylic acid (100) (substrate, Me2NCHO, POCI3, 0°C, 1 h, then 95°C, 6 h 69% note the hydrolysis of the ester grouping).876... 

Selective reduction of —COOH to —CHiOH. Chemoselective reduction of car-boxylic acids is possible by in situ conversion to the carboxymethyleneiminium salt by reaction with the Vilsmeier reagent (DMF and oxalyl chloride). This salt is then reduced with NaBH4 (2 equiv.) to the alcohol (equation I). Various functional groups are tolerated bromo, cyano, ester, and C=C (even when conjugated to COOH). 

Carboxylic acid chlorides. Conventional methods for conversion of an acid into the acid chloride usually require acidic reagents. Lederle chemists have accomplished this transformation under neutral conditions by conversion of the acid into the t-butyldimethylsilyl ester. The esters react with oxalyl chloride in CH2CI2 in the presence of catalytic quantities of DMF to form the acid chloride with evolution of gas. Since DMF is essential, dimethylformiminium chloride (Vilsmeier reagent) is probably the reactive species. The acid chloride is formed in 85-95% yield, as shown by conversion to esters with ethanol-pyridine. 

Azodicarboxylates undergo Michael addition to the electron-rich 5-position. The intermediate hydrazino ester is converted with bases to fervenu-lones or converted with Vilsmeier reagent (POCl3-DMF) to fervenulins, which are available by oxidation of the corresponding hydrazone using lead tetraacetate [75JOC2321 76JCS(P 1)2398] (Scheme 82). 

Condensation of 7-keto-ester hydrazones 475 with the Vilsmeier reagent yielded a general synthesis of l,3-diaryl-4-pyrazoleacetic acid esters 476 (Equation 95) <2005JHC131>. Regioselective addition of lithiated /3-hydrazono-phosphino oxides 477 to isocyanates afforded functionalized hydrazonoamides 478, which were then cyclized to 5-aminopyrazoles 479 with phosphorus oxychloride in the presence of triethylamine (Scheme 56) <1996T4123>. 

Recent literature refers to the stereoselective and asymmetric epoxidation of allylic alcohols with organoaluminium peroxides. PhaSiOOH epoxidizes olefins with a stereoselectivity similar to that with peracid. Reports have been made of a-substituted hydroperoxides (acids, esters, ketones, amides, and nitriles) as effective epoxidizing reagents and the application of hexachloroacetone, tetrachloracetone, and hexafluoroacetone hydroperoxide, as well as the HaOa-Vilsmeier reagent system. ... 

A -Aryl-iV -phenylalkynylamidines are cycitzed to quinolines by treatment with hot PPA the main product is the 2-(A -methyl-yV-phenylamino)quino]ine but cyclization on to the other benzene ring may (xxur to some extent. 3-Phenyl-aminobut-2-enoate esters are cyclized (on to a ring-carbon) at or below room temperature by the application of Vilsmeier reagents. 

The formamides 16 are intermediates. Formamide (Bredereck variant of the Traube synthesis [149]), formamidine, orthoformic ester, diethoxymethyl acetate, Vilsmeier reagent (fi om DMF and POCI3) and dithioformic acid are used as formic acid derivatives. 4,5-Diaminopyrimidines can be obtained from 4-aminopyrimidines 17 by nitrosation with HNO2 followed by reduction of the nitroso compounds 18 ... 

Conversion of BCOD-fused pyrrolecarboxylate ester 8 and its a-free derivative 9 could be easily accomplished by rich pyrrole chemistry (Scheme 15.4). The free a-positions of BCOD-fused pyrroles are so electrophilic that formylation and halogenation easily occurred. Formylation of 8 was achieved by both the Vilsmeier reagent (POCI3, DMF) and... 

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