Reactivity of (Z)-4-Aryliden-5(4H)-thiazolones: [2+2]-Photocycloaddition, Ring-Opening Reactions, and Influence of the Lewis Acid BF3

Sierra, S ; Dalmau, D (Universidad de Zaragoza) ; Higuera, S ; Cortes, D ; Crespo, O (Universidad de Zaragoza) ; Jimenez, AI ; Pop, A ; Silvestru, C ; Urriolabeitia, EP

Resumen: The irradiation of (Z)-2-phenyl-4-aryliden-5(4H)thiazolones 2 with blue light (465 nm) in CH2Cl2 solution promotes [2 + 2]-photocycloaddition of the exocyclic C=C bonds and the formation of the dispirocyclobutanes 3. This reaction takes place with high stereoselectivity, given that the epsilon-isomer (1, 3 head-to-tail syn coupling) is formed in more than 90% yield in most of the cases. However, irradiation of 5(4H)-thiazolones 2 with blue light (456 nm) in dry MeOH in the presence of BF3 center dot OEt2 leads to the monospirocyclobutanes 4 with full stereoselectivity, also affording the epsilon-isomer. A ring-opening reaction of only one of the thiazolone rings appears to have taken place in 4 upon methanolysis, leading to the corresponding ester and thioamide groups. The treatment of free 4-aryliden-5(4H)-thiazolones 2 with a base in alcohol (NaOR/ROH) also produces a ring-opening reaction of the heterocycle by methanolysis, although, under these reaction conditions, further intramolecular S-attack at the exocyclic C(H)=C bond and cyclization is observed, forming the dihydrothiazoles 5 or 6 as mixtures of cis (RS/SR)- and trans (RR/SS)-isomers with high diastereomeric excess. trans-(RR/SS)-Dihydrothiazoles 6 can be isolated as pure diastereoisomers by column chromatography. Surprisingly, dihydrothiazoles 5 can also be obtained by the treatment of 4-aryliden-5(4H)-thiazolones 2 with BF3 center dot OEt2 in methanol in the absence of a base.

Idioma: Inglés

DOI: 10.1021/acs.joc.1c01458

Año: 2021

Publicado en: Journal of Organic Chemistry 86, 17 (2021), 12119-12140
ISSN: 0022-3263

Factor impacto JCR: 4.198 (2021)

Categ. JCR: CHEMISTRY, ORGANIC rank: 12 / 57 = 0.211 (2021) - Q1 - T1

Factor impacto SCIMAGO: 0.983 - Organic Chemistry (Q1)

Financiación: info:eu-repo/grantAgreement/ES/DGA/E07-20R
Financiación: info:eu-repo/grantAgreement/ES/AEI/PID2019-104379RB-C21
Financiación: info:eu-repo/grantAgreement/ES/AEI/PID2019-106394GB-I00
Financiación: info:eu-repo/grantAgreement/ES/DGA/E19-20R

Tipo y forma: Artículo (Versión definitiva)

Área (Departamento): Área Química Inorgánica (Dpto. Química Inorgánica)