N‐Heterocyclic Carbene‐Catalyzed in situ Activation of Alkynyl Acids for C−S Bond Formation: Access to Imidazo[2,1‐b][1,3]thiazinones

Abstract

Alkynyl acids are first utilized as alkynyl acylazolium precursors through an in situ activation strategy for the efficient construction of carbon‐sulfur bond in a formal [3+3] annulation. This protocol offers a direct and rapid pathway for the synthesis of imidazo[2,1‐b][1,3]thiazinone skeleton, a useful heterocyclic class frequently found in many bioactive compounds. This reaction also has the advantages of scalability, readily available materials, and simple manipulation in open air.magnified image

Recent Progress toward the Construction of Axially Chiral Molecules Catalyzed by an N-heterocyclic Carbene

“…NHC-bonded alkynyl acyl azoliums 1 were found to be important intermediates for atroposelective annulation by reaction with bis-nucleophiles 2 − (Scheme ). In 2018, we disclosed the first example of NHC-catalyzed atroposelective annulation.…”

Recent advances of N-heterocyclic carbenes in the applications of constructing carbo- and heterocyclic frameworks with potential biological activity

“…situ to form C-S bond, leading to the corresponding [3 + 3] cycloadducts (Scheme 46a). 94 In 2019, Biju and co-workers reported their [3 + 3] cycloaddition between enals and thioamides 142 catalyzed by chiral NHC C21, resulting in a variety of functionalized thiazinones 143 with high stereoselectivities (Scheme 46b). 95 Thirty-two reactions were carried out to prove the good functional group applicability.…”

“…In 2018, imidazo fused thiazinones 141 was synthesized by Du et al In the presence of NHC C42 generated from the thiazolium, alkynyl acids were converted into alkynyl acylazolium intermediates, then reacted with mercaptoimidazoles 140 in situ to form C–S bond, leading to the corresponding [3 + 3] cycloadducts ( Scheme 46a ). 94 In 2019, Biju and co-workers reported their [3 + 3] cycloaddition between enals and thioamides 142 catalyzed by chiral NHC C21, resulting in a variety of functionalized thiazinones 143 with high stereoselectivities ( Scheme 46b ). 95 Thirty-two reactions were carried out to prove the good functional group applicability.…”

Donor–Acceptor Cyclopropanes as an Expedient Building Block Towards the Construction of Nitrogen‐Containing Molecules: An Update

“…[91] Wang et al utilized an intramolecular cross [3+ +2] cycloaddition (IMCC)r eactionf or the synthesiso f (AE)-pyrido[3,4-b]homotropane (PHT) 167 and (À)-PHT derivatives 168. [92] Ther eactions cheme for the synthesiso fP HT includesi nitial Sc(OTf) 3 -catalyzed intramolecular cross [3+ +2] cycloaddition (IMCC) of compound 161 to form compound 162.C ompound 162 is then subjectedt oaKrapcho decarboxylation to [93] Thep resent annulation involves as equence of ring opening/aromatization/nucleophilica ddition reactions. In this protocol, aromatizationi st he drivingf orce for the [3+ +4] annulation.…”