Three-Component Reactions of Alkynone o-Methyloximes, Element Selenium, and Boronic Acids Leading to 4-Organoselenylisoxazoles

Abstract

We report an Ag-catalyzed one-pot three-component reaction of alkynone o -methyloxime, element selenium, and boronic acid, providing a facile route to selenated isoxazole product. This protocol features high efficiency, wide substrate scope, and the use of selenium powder as the selenium source.

Silver-catalyzed three-component reaction of uracils, arylboronic acids, and selenium: synthesis of 5-arylselanyluracils

“…The aryl radical then reacts with selenium powder to form arylselanyl radical A , which immediately undergoes radical coupling to form diaryl diselenide B . 18,21 Diselenide B then receives one electron from Ag + to generate the aryl selenide anion C and A . Radical A then reacts with uracil 1 to produce intermediate D , which is then converted into 3-selenyluracil 5 via E and F .…”

“…Ag-catalyzed reactions are powerful tools for the formation of carbon–carbon and carbon–heteroatom bonds and are attracting increasing attention in modern organic chemistry. 17 Among these, Liu and co-workers developed Ag-catalyzed three-component reactions for C–Se bond formation using an arylboronic acid, Se powder, and an epoxide or acetylene derivative; 18–21 the reactions with epoxides catalyzed by AgNO 3 afford β-hydroxyselenides through epoxide ring-opening and selenation (Scheme 1a). 18 Reactions with 2-alkynyl-anisoles, -thioanisoles, -aryl esters, and alkynone O -methyloximes catalyzed by AgNO 3 and AgNO 2 gave furan and thiophene derivatives, isochromenones, and isoxazoles through the tandem cyclization and selenation (Scheme 1b and c).…”

“…18 Reactions with 2-alkynyl-anisoles, -thioanisoles, -aryl esters, and alkynone O -methyloximes catalyzed by AgNO 3 and AgNO 2 gave furan and thiophene derivatives, isochromenones, and isoxazoles through the tandem cyclization and selenation (Scheme 1b and c). 19–21 Clearly, the use of Se powder, which is commercially available, stable, and easy-to-handle, as a reagent for the construction of C–Se bonds provids a more straightforward and attractive alternative. However, the previous methods used either for ring-opening reactions of epoxides or for electrophilic annulation reactions to form heterocycles.…”

Synthesis of Organoselenium Compounds with Elemental Selenium

“…The reactions to generate selenated isochromenones were compatible with a wide range of alkynylaryl esters and successfully scaled up to 10 mmol scale (Scheme 13a) [26a] . Meanwhile, the reaction to afford selenated isoxazoles exhibited good efficiency towards a wide variety of electronically boronic acids including arylboronic acids and alkylboronic acids (Scheme 13b) [26b] …”

Synthesis of 2,5-disubstituted selenophenes via a copper-catalyzed regioselective [2+2+1] cyclization of terminal alkynes and selenium

“…As a readily available and non-toxic selenium source, elemental selenium is an important synthon in the field of organic synthesis, which has been applied to the construction of various organoselenium compounds through cross-coupling reactions, cycloaddition reactions, insertion reactions, etc. 1–3 However, the incorporation of elemental selenium to build selenium-containing heterocycles with specific characteristics and useful properties is still faced with challenges since selenium is usually difficult to be activated and the chemoselectivity issue needs to be addressed. 4…”