Dehydro formaldehyde

Reaction of thienopyrimidinediamines 45 with formaldehyde in the presence of hydrochloric acid gives 3,4-dihydro-57f-l-thia-3,5,6,8-tetraazaacenaiAthalenes 46. The use of triethyl orthoformate gives the 3,4-dehydro products <95LA1703 96KGS103 96CA(125) 167905 >. 

Dihydro-1,3-benzoxazines (196) are formed by the reaction of phenols with a mixture of formaldehyde and primary aromatic amines in the molar ratio 2 1. Presumably the phenol first reacts with the appropriate iminium species to form an intermediate amine (195), which is then cyclized in a Pictet-Spengler type reaction (Scheme 81) (44JA1875). If 2-hydroxybenzylamines are employed then methylene derivatives are obtained, and if the formaldehyde is replaced by a-dicarbonyl compounds dehydro dimers (197) are produced (Scheme 82) <70BCJ226>. 

Acid-catalysed hydrolysis of pycnanthinine (195) gives (+)-pleiocarpamine (196), (—)-6,7-dehydro-aspidospermidine (211), and formaldehyde. Reductive... 

Benzylparaben, bromochlorophene, butylparaben, chlorophene, chloroxylenol, chlorphenesin, cloflucarban, dichlorobenzyl alcohol, dichlorophene, ethylparaben, hexachlorophene, isopropyl sorbate methylparaben, o-cymen-5-ol, o-phenylphenol, p-chloro-ra-ciesol, phenoxyethanol, tetrabromo-o-cresol, triclocarban, triclosan BenzaUconium chloride (a), formaldehyde (b), sodium dehydro acetate (c)... 

Benzo-l,3>thiazines.—A direct procedure for preparing 2,3-dehydro-4H-l,3-benzothiazines is afforded by the condensation of 2-mercaptobenzylamine and its derivatives with ketones or aldehydes in alkaline medium. Thus, for example, (46) reacts with acetaldehyde to give (47 R = Me) in excellent yields. A somewhat different course is observed in the condensation of (46) with formaldehyde, which gives the methylene bis-derivative (48), resulting from the fast reaction of the primary product (47 R = H) with more of the aldehyde. 

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