Silver(I)-Catalyzed Regioselective Synthesis of Triazole Fused-1,5-Benzoxazocinones

Abstract

An efficient and regioselective synthesis of novel 1,2,3-triazole-fused-1,5-benzoxazocinones through intramolecular cyclization of substituted ethynyl triazoyl benzoic acids was explored. A crucial precursor 5-iodo-1,2,3-triazole benzoate was obtained from substituted 2-azido benzoic acid esters in a single step through a Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) reaction using a CuI/NBS catalytic system. A carbon-carbon triple bond was installed through a Sonogashira coupling reaction by various terminal alkynes. Finally, the 1,4,5-substituted ethynyl triazoyl benzoic acids were cyclized by a AgOTf-mediated intramolecular cyclization to afford 8-endo-dig 1,2,3-triazole-fused-1,5-benzoxazocinones exclusively.

1-Iodobuta-1,3-diynes in Copper-Catalyzed Azide–Alkyne Cycloaddition: A One-Step Route to 4-Ethynyl-5-iodo-1,2,3-triazoles

“…It is important that both types of products, triazole-fused enediynes and 5-aryl-4-ethynyltriazoles, are of special importance because of possible further intramolecular cyclizations known for other types of benzene­(heteroarene)-fused enediynes − and ortho -ethynylaryl-substituted arenes, − leading to highly conjugated polyaromatic compounds. Among such systems, polycyclic fused 1,2,3-triazoles are of particular interest. − …”

“…We started with the synthesis of enediynes. Remarkably, a triple bond has been introduced into position 5 of a triazole ring mostly using the Sonogashira coupling, ,− yet several examples for the synthesis of 4-aryl-5-ethynyl-1,2,3-triazole using one-pot CuAAC/ethynylation have also been reported. − …”

Progress in the Synthesis of Fused 1,2,3‐Triazoles

“…Sun and group developed regioselective exclusive synthesis of 8‐ endo ‐ dig 1,2,3‐triazole‐fused‐1,5‐benzoxazocinone derivatives 336 from substituted ethynyl triazoyl benzoic acids 335 via silver triflate mediated intramolecular cyclization in good yields (Scheme 106). [106] …”

A Route to Triazole-Fused Sultams via Metal-Free Base-Mediated Cyclization of Sulfonamide-Tethered 5-Iodotriazoles

“…Among them, 5-iodotriazoles are of special significance due to the ease of further functionalization via metal-catalyzed substitution reactions (Scheme ). These compounds were extensively used in various Pd-catalyzed processes including Suzuki, − Stille, − Heck, ,, Sonogashira, ,,, and carbonylation reactions. Cu-catalyzed post-Ullmann chemistry was used to replace the iodine atom by S-, , O-, and N-nucleophiles …”