Paraformaldehyde, condensation with

Palladous chloride in preparation of hydrogenation catalyst, 46, 89 Paraformaldehyde, condensation with propiophenone, 48, 91 conversion to formaldoxime, 46,13 Pelargonyl fluoride, 45, 6 1-Pentalenecarboxylic acid, octa-IIYDRO-, 47, 10... 

Palladized strontium carbonate, 44, 37 2.2]Paracyclophane. 42, 83 Paraformaldehyde, condensation with nitromethane, 41, 67... 

Two syntheses of 1,3-benzodioxans lead to a wide variety of products. The substituted salicylic ester (200) on heating with chloromethyl methyl ether gave a mixture of the phenol (201 R=H) and its ether (201 R=CH2C1) in 52 and 12% yield, respectively.207 Paraformaldehyde condensed with 4-hydroxyacetophenone and Amberlite IR120 to yield the two benzodioxans (202) and (203) in various proportions.208... 

Propanol with magnesium in reduction of chlorobenzene, 47, 104 Propionic acid, 2-(2,4,5,7-tetranitro-flcoken-9-ylideneamtnooxv)-, (+)- AND (-)-, 48, 120 Propionyl fluoride, 45, 6 Propiophenone, condensation with paraformaldehyde, 48, 91 -Propylaminc, 45, 85 -Propylhydrazine, 45, 85 C-( -Propyl)-N-phenylnitrone, generation from phenylhydroxylamine and -butyraIdehyde, 46, 97 Purification of tetrahydrofuran (Warning), 46,105 477- Pyran-4-0ne, 2-6-dimethyl-3,5-DIPHENYL-, 47, 54... 

Diamines, aminothiols, and aminoalcohols are well suited for quantitative solid-state cyclizing condensations with simple aldehydes and ketones. As yet only quantitative gas-solid reactions with acetone and solid-solid reactions with paraformaldehyde (that will monomerize upon the milling) have been profited from. An early remarkable reaction type involving two molecules of... 

B as an ester- or lactone-substituted aldehyde enolate. Such enolates undergo condensations with all kinds of aldehydes, including paraformaldehyde. An adduct E is formed initially, acy-lating itself as soon as it is heated. The reaction could proceed intramolecularly via the tetrahedral intermediate D or intermolecularly as a retro-Claisen condensation. In both cases, the result is an acyloxy-substituted ester enolate. In the example given in Figure 13.50, this is the formyloxy-substituted lactone enolate C. As in the second step of an Elcb elimination, C eliminates the sodium salt of a carboxylic acid. The a,/)-unsaturated ester (in Figure 13.50 the 0J,/3-unsaturated lactone) remains as the aldol condensation product derived from the initial ester (here, a lactone) and the added aldehyde (here, paraformaldehyde). 

It also can be produced directly from natural gas, methane, and other aliphatic hydrocarbons, but this process yields mixtures of various oxygenated materials. Because both gaseous and liquid formaldehyde readily polymerize at room temperature, formaldehyde is not available in pure form. It is sold instead as a 37 percent solution in water, or in the polymeric form as paraformaldehyde [HO(CH20)nH], where n is between 8 and 50, or as trioxane (CH20)3. The greatest end use for formaldehyde is in the field of synthetic resins, either as a homopolymer or as a copolymer with phenol, urea, or melamine. It also is reacted with acetaldehyde to produce pentaerythritol [C(CH2OH)4], which finds use in polyester resins. Two smaller-volume uses are in urea-formaldehyde fertilizers and in hexamethylenetetramine, the latter being formed by condensation with ammonia. 

Condensations of bis(o-mercapto)phenyl sulfide with paraformaldehyde or diiodomethane in moderately concentrated solutions gave dibenzo[//,g][l,3,6]trithiocine 56 in 28—49%> yields, accompanied with 6-10% yields of the product of 2 2 condensation, hexathiacyclohexadecine 131 (Scheme 33). Condensation with diiodomethane in diluted solution afforded trithiocine 56 as a sole product in 90% yield. Interestingly, when carbonyl or thiocarb-onyl diimidazoles were used as dielectrophile, formation of a 16-membered ring was predominant and the eight-membered product 132 was not observed <1999H(50)103>. 

Vinyl ketones. Methyl ketones (1) undergo a Mannich-type condensation with paraformaldehyde (2), when refluxed in THF or dioxane in the presence of N-methylanilinium trifluoroacctate (this volume) to give vinyl ketones. The only... 

The enhanced activity of alkyl groups attached to the pyrazine nucleus is illustrated by methylpyrazine, which undergoes aldol type condensations with aldehydes and ketones. Methylpyrazine (14) formed an adduct (IS) with chloral in pyridine solution (405) with paraformaldehyde at 165°, it gave 2-hydroxyethylpyrazine (470) (which was subsequently dehydrated with molten potassium hydroxide to 2-vinylpyrazine) and with benzophenone and sodamide it gave the corresponding carbinol (705). 

During the enantioselective total synthesis of (-)-coriolin, I. Kuwajima and co-workers used a Darzens-type reaction to construct the spiro epoxide moiety on the triquinane skeleton. Interestingly, the usual Darzens condensation where the a-bromoketone was condensed with paraformaldehyde yielded a bromohydrin in which the hydroxymethyl group was introduced from the concave face of the molecule. This bromohydrin upon treatment with DBU gave the undesired stereochemistry at C3 (found in 3-ep/-coriolin). To obtain the correct stereochemistry at C3, the substituents were introduced in a reverse manner. It was also necessary to enhance the reactivity of the enolate with potassium pinacolate by generating a labile potassium enolate in the presence of NIS. The in situ formed iodohydrin, then cyclized to the spiro epoxide having the desired stereochemistry at C3. 

Formaldehyde can be used as an aqueous solution, as paraformaldehyde or, if needed and useful for the desired products, condensed with ammonia (e.g., in... 

These systems are reported as cyclopentaoxazolidines and can be obtained by conventional azeotropic dehydration of aldehydes with amino alcohols <85TL5303> for example, (S)-5-Hydroxymethyl-2-pyrrolidinone (236) was condensed with benzaldehyde to obtain the corresponding chiral 5-oxo-2-phenylperhydropyrrolo[l,2-c]oxazole (237) in excellent yield <86JOC3140>. Similar treatment of enantiomerically pure amino ketone (238) with paraformaldehyde or formalin under a variety of Mannich conditions yielded (239) <84ja5360>. These reactions are shown in Scheme 41. 

The 4,7-dimethyl-substituted 4,7-dihydro-l, 3-dithiepin (220) could be obtained by LAH reduction of ne50-hex-3-en-2,5-diyl dithiocyanate (219) and treatment with paraformaldehyde (Equation (40)) <93CC246>, and 2-alkylidene-4,7-dihydro-1,3-dithiepins, for example (222), which are useful as pharmaceutical intermediates, have been synthesized by reaction of C—H acidic substrates with sodium hydride, followed by condensation with CS2 and cyclization of intermediate (221) with (Z)-l,4-dichloro-2-butene (Scheme 37) <85GEP228255, 86JPR215>. 

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