doi:10.1021/acs.joc.1c01458engSierra, SDalmau, DHiguera, SCortes, DCrespo, OJimenez, AIPop, ASilvestru, CUrriolabeitia, EPReactivity of (Z)-4-Aryliden-5(4H)-thiazolones: [2+2]-Photocycloaddition, Ring-Opening Reactions, and Influence of the Lewis Acid BF3ART-2021-126397The 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.2021http://zaguan.unizar.es/record/11965710.1021/acs.joc.1c01458http://zaguan.unizar.es/record/119657oai:zaguan.unizar.es:119657info:eu-repo/grantAgreement/ES/DGA/E07-20Rinfo:eu-repo/grantAgreement/ES/AEI/PID2019-104379RB-C21info:eu-repo/grantAgreement/ES/AEI/PID2019-106394GB-I00info:eu-repo/grantAgreement/ES/DGA/E19-20RJournal of Organic Chemistry 86, 17 (2021), 12119-12140byhttp://creativecommons.org/licenses/by/3.0/es/info:eu-repo/semantics/openAccess