BF₃·Et₂O-Promoted Cleavage of the C_sp–C_sp2 Bond of 2-Propynolphenols/Anilines: Route to C2-Alkenylated Benzoxazoles and Benzimidazoles

Abstract

A novel BF3·Et2O-promoted tandem reaction of easily prepared 2-propynolphenols/anilines and trimethylsilyl azide is developed to give C2-alkenylated benzoxazoles and benzimidazoles in moderate to good yields. Most reactions could be accomplished in 30 min at room temperature. This tandem process involves a Csp-Csp2 bond cleavage and a C-N bond formation. Moreover, both tertiary and secondary propargylic alcohols with diverse functional groups were tolerated under the mild conditions.

Catalytic Carbonylative Double Cyclization of 2-(3-Hydroxy-1-yn-1-yl)phenols in Ionic Liquids Leading to Furobenzofuranone Derivatives

“…HRMS (ESI-TOF) m / z : [M + Na] + calcd for C 16 H 14 O 2 Na + , 261.0886; found, 261.0879. The spectroscopic data agreed with those reported …”

BF3·OEt2-AgSCF3 Mediated Trifluoromethylthiolation/Cascade Cyclization of Propynols: Synthesis of 4-((Trifluoromethyl)thio)-2H-chromene and 4-((Trifluoromethyl)thio)-1,2-dihydroquinoline Derivatives

“…With multistep reactions combined into one synthetic operation, cascade cyclization proved to be a powerful strategy for the synthesis of cyclic compounds . By taking into consideration our current interest in introducing fluorine-containing groups, , as well as the continued anticipation of new approaches to skeletons of natural products, we designed a Lewis acid mediated trifluoro­methyl­thiolation–cyclization of propynols with AgSCF 3 . This paper reported the direct trifluoro­methyl­thiolation–cyclization reaction proceeds along an anion pathway, with a 2 H -chromene or 1,2-dihydro­quinoline system constructed in a single step simultaneously.…”

“…A plausible mechanism that is consistent with the experimental results mentioned above and the precedent literature is proposed in Scheme . In fact, the propargyl hydroxy group of substrate 1 is initially activated by BF 3 ·OEt 2 and generates propargylic cation A , which would undergo a subsequent tautomerism to generate the allenic cation B . , The intermolecular attack of the SCF 3 anion onto B affords intermediate C , which could be activated by Ag­(I) species or a proton to give intermediate D .…”

Recent Advances in the Synthesis of Heterocyclics via Cascade Cyclization of Propargylic Alcohols

“…To expand the application of the above methodology in the construction of such compounds, they designed 2‐propynophnols/anilines 136 as substrates to conduct the reaction in the presence of BF 3 ⋅OEt 2 (Scheme 53). [72] A variety of substituted benzoxazoles and benzimidazoles 137 were successfully constructed in good yields. In this transformation, the intermediate E (Scheme 52) was trapped by an intramolecular nucleophilic group (hydroxy or amino group) rather than intermolecular TMSN 3 to give the target products 137 .…”