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New and efficient methods for the synthesis of 7-substituted- 4-trifluoromethylpyrimido[1,2-b]pyridazin-2-one derivatives using either two-step Suzuki/heterocyclization, or two-step heterocyclization/substitution sequences are developed. A variety of substituted products are obtained in good to excellent yields from 3-amino-6-chloropyridazine and ethyl 4,4,4-trifluorobut-2-ynoate. [ABSTRACT FROM AUTHOR]

2,2'-Bithiophene and halogenated-2,2'-bithiophenes were halogenated with 2-halo-4,5-dichloropyridazin-3(2 H)-one in the presence of zinc halide to give selectively the corresponding dihalo-, trihalo-, and tetrahalo-2,2'-bithiophenes involving the same or different halogens in excellent yields, respectively. [ABSTRACT FROM AUTHOR]

Phenanthridines and azocines fused to two benzene rings or one benzene and one pyridazinone ring, which are otherwise difficult to access, were prepared via two new extensions of the tert-amino effect. The synthetic pathway includes three steps: i) Suzuki reaction of an ortho-functionalized phenylboronic acid with ortho-disubstituted benzenes or pyridazinones; ii) the Knoevenagel condensation reaction of the biaryl aldehydes formed with active methylene compounds to obtain vinyl derivatives or, through their cyclization, phenanthridines via a tert-amino effect; and iii) thermal isomerization of vinyl or phenanthridinium compounds to fused azocines via another type of tert-amino effect. [ABSTRACT FROM AUTHOR]

Phenanthridines and azocines fused to two benzene rings or one benzene and one pyridazinone ring, which are otherwise difficult to access, were prepared via two new extensions of the TERT-amino effect. The synthetic pathway includes three steps: i) Suzuki reaction of an ORTHO-functionalized phenylboronic acid with ORTHO-disubstituted benzenes or pyridazinones; ii) the Knoevenagel condensation reaction of the biaryl aldehydes formed with active methylene compounds to obtain vinyl derivatives or, through their cyclization, phenanthridines via a TERT-amino effect; and iii) thermal isomerization of vinyl or phenanthridinium compounds to fused azocines via another type of TERT-amino effect. [ABSTRACT FROM AUTHOR]

The synthesis of a novel class of 6-amino-5-hydroxy?pyridazin-3(2 H)-ones (3-oxo-2,3-dihydropyridazines) is described. These compounds also contain an ethoxycarbonyl moiety at the 4-position of the pyridazinone ring. They are prepared in good to moderate yields (30-72%) by the condensation of disubstituted amines with (alkylhydrazono)- or (arylhydrazono)(chloro)acetates followed by subsequent acylation with ethyl malonyl chloride and Dieckmann cyclization. An initial assessment of the scope and limitations of the new methodology is described along with the novel synthesis of several (alkylhydrazono)(chloro)acetate substrates utilized in the pyridazinone preparations. [ABSTRACT FROM AUTHOR]

2,6-Disubstituted 5-hydroxy-3(2 H)-pyridazinone-4-carboxylic acid ethyl esters were synthesized from ?-keto esters via an efficient three-step sequence including hydrazone formation, acylation with ethyl malonyl chloride, and subsequent Dieckmann cyclization. [ABSTRACT FROM AUTHOR]

2,4,5-Trichloro- (2a) and 2,4-dichloro-5-methoxypyridazin- 3(2H)-one (2b) are novel electrophilic chlorinating agents. a-Chlorination of active methylene/methine compounds with 2 in the presence of either Lewis or protonic acids in dichloromethane (for Lewis acid) or water (for protonic acid or none) at room temperature gave also selectively α-monochlorides and/or a,a-dichlorides in good to excellent yields. [ABSTRACT FROM AUTHOR]