Regioselective photocyclization of (e)-2-(2,3,6-trichlorostyryl)-benzothiazole and synthesis of 3,4-dichloro- and 4-chlorobenzothiazolo[3,2-α]quinolinium chlorides: A synthetic and theoretical study

Autor: Marisol Cordero, Carmelo Garcia, Osvaldo Cox
Rok vydání: 2008
Předmět:
Zdroj: Journal of Heterocyclic Chemistry. 45:1255-1264
ISSN: 1943-5193
0022-152X
DOI: 10.1002/jhet.5570450501
Popis: A high degree of regioselectivity is observed in the photochemically induced cyclization of (E)-2-(2,3,6-trichlorostyryl)benzothiazole (1a). According to the proposed mechanism, this compound was expected to afford two products, 3,4-dichloro- and 1,4-dichlorobenzothiazolo[3,2-α]quinolinium chlorides (4a and 4a', respectively). However, this reaction produced 3,4-dichlorobenzazolo[3,2-α]quinolinium chloride (4a) as the sole product. On the other hand, irradiation of (E)-2-(2,3,5-trichlorostyryl)benzothiazole (1b) failed to produce the expected 1,3-dichlorobenzothiazolo[3,2-α]quinolinium chloride (4b). Furthermore, (E)-2,3-difluorostrylbenzothiazole (1c) also failed to give the corresponding 1-fluorobenzothiazolo[3,2-α]quinolinium fluoride (4c). Interestingly, the irradiation of 2,6-dichlorostyrylbenzothialole (1d) produced 4-chlorobenzothiazolo[3,2-α]quinolinium chloride (4d) in excellent yield. This paper presents the results of these investigations and a mechanistic rationale for the outcome of this reaction based on steric arguments and theoretical studies using a combination of molecular mechanics (MM+) and semiempirical quantum mechanical calculations (PM3/RHF/CI). Two-dimensional high field nmr methods were employed to make complete assignments of the proton and carbon spectra of all new compounds.
Databáze: OpenAIRE
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