Ring Opening of Dihydro-1,4-oxathiins

Abstract

Acid hydrolysis of 5,6-dihydro-2-methyl-I,4-oxathiin-3-carboxanilide gives 2-(2-hydroxyethy1thio)-acetoacetanilide enol. 3-Carbonyl-substituted 5.6-dihydro-l,4-oxathiins were found to undergo ring cleavage by nucleophilic nitrogen attack on C-2. Thus the following reactions were observed: 3-acetyl-5,6-dihydro-2-methyl-1,4-oxathiin o n treatment with hydrazine gives 4-(2-hydroxyethylthi0)-3,5-dimethylpyrazole, instead of the hydrazone. The 1,4-oxathiins, N-(5,6-dihydro-2-methyl-1,4-oxathiin-3-ylcarbony1)-N'-phenylurea and 5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxylic acid hydrazide rearrange to give 5-(2-hydroxyethy1thio)-6-methyl-I-phenylracil and 4-(2-hydroxyethy1thio)-3-methyl-2-pyrazolin-5-one, respectively. Finally, treatment of 5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl chloride with 2-aminopyridine and with 2-aminopyrimidine affords 4H-3-(2-hydroxyethy1thio)-2-methylpyrido[l,2-nlpyrimidin-4-one and 4H-3-(2-hydroxyethylthio)-2-methylpyrimido[l,2-a]pyrimidin-4-one, respectively, a s the predominant products.

Fungicidal Activity of Aromatic Ketone Pyrimidinylhydrazones

“…The E-isomers showed greater activity in vitro than the related Z-isomers, but the difference was very little between the isomers in vivo as was observed in a series of aromatic aldehydes. 2' In order to clarify the scope and limitation of aromatic substitution, substituents (2)(3)(4)(5)(6)(7)(8)(9)(10)(11), such as halogens, alkyl, trifluoromethyl and nitro groups were introduced singly into the 2'-position on the aromatic ring at the beginning while the pyrimidine ring was substituted with two methyl groups in the 4-and 6-positions ( Table 1). The 2'-methyl derivative (8) was the most active of the three mono-substituted derivatives (2,8,10), which showed excellent activity against rice blast in vivo.…”

Glass-catalyzed decomposition of oxycarboxin in aqueous solution

“…by a similar reaction reported for the ring-opened form of carboxin (Corbeil et al, 1973). It is proposed that the silanol groups available at the glass surface act as a base to catalyze the ring-opening step.…”

“…It was shown by others that oxycarboxin is susceptible to acid-catalyzed hydrolysis (Corbeil et al, 1973) and basecatalyzed hydrolysis (Kulka, 1980). Although both carboxin and oxycarboxin would be susceptible to hydrolysis, the carboxin solutions appeared to be stable while the solutions of oxycarboxin were not.…”

A New Synthesis of 1,4-Thiazin-3-ones by a Novel Rearrangement of 1,4-Oxathiins

“…The mechanism for the rearrangement can be explained as follows. Protonation of the amide carbonyl in 3 followed by addition of water resulted in hemiacetal 4 which can undergo a ring-opening to provide 5 . Protonation of the newly formed carbonyl in 6 can result in trapping of the carbenium ion by either the lone pair on nitrogen (path a) or the oxygen of the enol form of the amide (path b) .…”