Alkynyl-λ(3)-iodanes have been established as alkynyl cation equivalents for the alkynylation of carbon- and heteroatom-based nucleophiles. Herein, we report an unprecedented reaction mode of this compound class, which features a Pd(II)-assisted 1,2-I(III) shift of an alkynylbenziodoxole. A Pd(II) catalyst mediates this shift and the subsequent interception of the transient vinylidene species with carboxylic acid (1,1-hydrocarboxylation). The product of this stereoselective rearrangement-addition reaction, β-oxyalkenylbenziodoxole, represents a novel and useful building block for further synthetic transformations.

We report herein the synthesis of highly substituted and stereochemically well-definedv inylbenziodoxole (VBX) derivatives through hydrochlorination and iodochlorination of ethynylbenziodoxoles.T he hydrochlorination is achieved using pyridine hydrochloridea sa nH Cl source in an anti-fashion under mild, open-air conditions to afford a2 -chlorinatedV BX product, which serves as a useful building block for the stereoselective synthesis of trisubstituted alkenes.M eanwhile, iodochlorination with iodine monochloride proceeds in an unusual syn-pathway, stereoselectively affording at etrasubstituted VBX derivative.Hypervalent iodine compounds bearing benziodoxol(on)e (BX) backboneh ave emerged as versatile electrophilic group-transfer agentsi no rganic synthesis, as the cyclic BX moiety endows the reagents with well-balanced stabilitya nd reactivity suited under broad range of reactionc onditions. [1] Amongv arious BX-based group transferr eagents, ethynyl-BXs( EBXs) have found numerous applicationsi nC -alkynyl and heteroatom-alkynyl bond formationss ince the pioneering work of Waser. [1a-d, 2-4] Meanwhile,t his class of compounds has also found unique synthetic applications beyonds imple alkynyl group transfer,i nw hich the BX group does not act as am ere leaving group but as an integralp art of the product. [5] In this context,E BXs have been found to serve as ap recursor to functionalized vinyl-BXs (VBXs), whichw ould serve as novel alkenyl group-transfer agents that are otherwise difficultt oa ccess. We disclosed palladium-catalyzed 1,1-hydrocarboxylation of various substituted EBXs by a1 ,2-iodine(III) shift, affordingV BXs bearing an enol carboxylate moiety (Scheme 1a). [6,7] Miyake reported anti-addition of phenols to aryl-EBXs under visible-light irradiation (Scheme 1b), in which the primary VBX product readily transforms into iodovinylether. [8] More recently,W aser has found simple conditions that allow fort he anti-addition of sulfonamides and phenolst oa lkyl-EBXs with retention of the BX moiety in the products. [9,10] As highly functionalized VBX compounds hold promise as versatile synthetic building blocks for stereodefined alkenes, [11] furtherd evelopment of EBX-to-VBX transformations is highly desirable.Herein, we report on stereoselective hydrochlorination and iodochlorination reactions of EBX, affording stereochemically well-defined halogenated VBX compounds (Scheme1c). The formerr eactionw as achievedu sing pyridineh ydrochloride in an exclusive anti-fashion, affording au seful buildingb lock for the stereoselective synthesiso fm ultisubstituted alkenes. The latter reactionu sing iodine monochloride features an unusual syn-addition pathway,a ffording an exotic tetrasubstituted VBX product.Hydrochlorination of haloalkynes offers as traightforward approacht oward synthetically useful 1,2-chlorohaloalkenes. Zhu and Xu independently achieved anti-hydrochlorinationo fh aloalkynes with LiCl/HOAc using palladium and gold catalysts, respectively, [12] which likely involved anti-chlorometalation of the C...