(Z)-β-Aryloxyalkenylzincs are synthesized stereoselectively via anti-carbozincation among alkynyl ethers, silyl ketene acetals, and ZnBr. X-ray analysis revealed the structure of the zinc species is a mononuclear two-coordinate dialkenylzinc that is transformed into functionalized enol ethers as a single isomer in the reaction of various electrophiles.
A simple procedure for the intermolecular enantioselective palladium-catalyzed decarboxylative allylation of β-ketoacids is described. This method, inspired by a stoichiometric control experiment performed by Saegusa and co-workers some 40+ years ago, makes use of allyl carbonates as the coupling substrates and enables direct access to α-allylated ketones bearing newly formed quaternary stereocenters. Experiments suggest that the transformation proceeds via an inner-sphere mechanism and not the traditional outer-sphere process proposed. The reaction should be highly useful and its application is demonstrated by a short enantioselective synthesis of (+)-adalinine.
The regioselective anti-carboindation of ynamides by usingI nBr 3 and silylated nucleophilesw as developed to synthesize (Z)-b-(carbonylamino)alkenylindiums. The X-ray crystallographic analysis of an alkenylindium suggested that the reaction proceeded in an anti-addition fashion.I nc ontrastt or eported syn-carbometalationso f ynamides by using organometallics, ac ooperation of InBr 3 and silylated nucleophiles to ynamides achieveda nantiaddition, whichw as supportedb yD FT calculations. The scope of substrates included variousy namides and silylated nucleophiles, such as silyl ketenea cetals and silyl ketene imines. The transformation of synthesized alkenylindiumsb yi odination,r adicalc oupling, and Pd-catalyzed cross-couplings uccessfully afforded trisubstituted enamines with high regio-and stereoselectivities.Enamides are versatile buildingb locks for valuable nitrogencontaining compounds. [1] Ac ombinationo fc arbometalations of ynamides and transformations of the formed metalated enamides is one of the most reliable synthetic methods for multisubstituted enamides. [2] In this strategy,e stablishmento fr egioand stereoselective carbometalation is necessary for selectively synthesizing ad esired enamide among possiblei somers. Syncarbometalation of ynamides of organometallic compounds has been widely studied (Scheme1a). For example, a-(carbonylamino)alkenylmetals are obtained through the syn-addition of organocoppers, -zincs,a nd -lithiums to ynamides. [3,4] In contrast, b-(carbonylamino)alkenylmetalsa re obtained by syn-carbopalladation of ynamides by using organopalladiums. [5] How-ever, anti-carbometalation of ynamides remains underdeveloped,a lthough the intramolecular carbometalations of ynamidesh ave been reported (Scheme 1b). [6] We recently reported intermolecular anti-carbometalations of carbon-carbon triple bonds by using silylatedn ucleophiles and metal salts, such as InBr 3 ,G aBr 3 ,A lBr 3 ,B iBr 3 ,a nd ZnBr 2 . [7] Therefore, we assumedo ur strategy could achieve anti-carbometalation of ynamides. Here, we report the anti-carbometalation of ynamides by using InBr 3 and silyl ketene acetals to synthesize (Z)-b-(carbonylamino)alkenylindiums(Scheme 1c).First, we surveyed metal halides fort he carbometalation of N-ethynylpyrrolidone (1a)b yu sing the silyl ketene acetal 2a (Table 1). The reactiono fy namide 1a by using InBr 3 and 2a followed by the addition of MeOH exclusively gave the product 3aa in 96 %y ield, where the carbon-carbon bond was formed at the carbon atom adjacent to the nitrogen atom (Table 1, entry 1). This results howed that enamide 3aa was produced by the protonationo fb-(carbonylamino)alkenylindium (detailsa re described below). Notably,r egioisomers obtainedf rom a-(carbonylamino)alkenylindiumsw ere not found despite the existenceo fa na mide moiety,w hich often serves Scheme1.Carbometalation of ynamides. Entry YnamideProduct [b] Entry YnamideP roduct [b] 1 4 2 5 3 6[a] InBr 3 (0.5 mmol), 1 (0.5 mmol), 2a (1.5 mmol), CH 2 Cl 2 (1 mL), I 2 (1.5 mmol), and DMF (1.5 mL).[b] Y...
We achieved regio- and stereoselective carboindation of terminal and internal alkynyl ethers using InI3 and organosilicon or -stannane nucleophiles to synthesize (Z)-β-alkoxyalkenylindiums. The carbometalation regio- and stereoselectively proceeded in anti-addition fashion, which was confirmed by X-ray diffraction analysis of (Z)-β-alkoxyalkenylindium products. Theoretical calculation on the carboindation of alkynyl ethers to elucidate the effect of an alkoxy group was conducted in parallel with calculations on a carbon analogue of the alkynyl ether. Reaction profiles and computational data of carboindation suggest that the alkoxy group enhances the interaction between InI3 and an alkyne moiety and reduces the activation energy. Many types of carbon nucleophiles such as silyl ketene acetals, silyl ketene imines, a silyl cyanide, an alkynyl stannane, and an allylic stannane were applicable to the present reaction system to give highly functionalized metalated enol ethers (β-alkoxyalkenylindiums). The prepared β-alkoxyalkenylindiums were transformed to various functionalized tetrasubstituted enol ethers by iodination followed by Suzuki coupling. The synthesis of a seven-membered ring compound containing a phenol ether moiety was accomplished using a sequential process that included the present stereoselective carboindation.
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