[雙語翻譯]應用化學外文翻譯--一種方便的合成氨基甲酸酯硒的方法（英文）

1、SHORT COMMUNICATIONDOI: 10.1002/ejoc.201301248Oxidative C–Se Coupling of Formamides and Diselenides by Using Aqueous tert-Butyl Hydroperoxide: A Convenient Synthesis of SelenocarbamatesPushpinder Singh,[a] Aanchal Batra,

2、[a] Paramjit Singh,[a] Amarjit Kaur,[a] and Kamal Nain Singh*[a]Keywords: Oxidation / Coupling reactions / Reaction mechanisms / Selenium / C–H activationAn oxidative coupling reaction between formamides and di- selenide

3、s under metal-free conditions is described. The C–Se bond formation occurred exclusively at the carbonylIntroductionDirect C–H functionalization of heteroatom-containing compounds by cross-dehydrogenative coupling (CDC)

4、is one of the most efficient routes for C–C bond formation and has been used for the synthesis of versatile building blocks and biologically active natural products.[1] The ad- vantage of using non-functionalized substra

5、tes makes this procedure more effective with wider applicability.[2] In the recent past, several efficient methods for C–H activation α to nitrogen and oxygen atoms have been developed under both transition-metal (e.g.,

6、Cu, Fe and Ru)-catalysed and metal-free conditions.[3,4] Many reports also describe the formation of C–N, C–P, C–O and C–S bonds by using CDC procedures.[5] However, C–Se bond formation by direct C– H selenylation has re

7、ceived very little attention and is lim- ited to metal-catalysed reactions of electron-rich arene or indole C–H bonds with diaryl selenides.[6] Other metal-cata- lysed reactions of diselenides, selenols or selenohalides

8、with substrates such as alkyl halides, alkynes, organoboranes and organosilanes have also been explored in the synthesis of organoselenides of biological and pharmaceutical impor- tance and with applications in materials

9、 science.[7] However, the metal-catalysed reactions are generally accompanied by toxic metal impurities along with pharmaceutically impor- tant final products[8a–8c] and the mechanistic pathways are usually complicated.[

10、8d] Thus, from the perspective of de- veloping an efficient and greener methodology by using simple reaction conditions, a metal-free approach to direct C–Se bond formation would be an attractive strategy.[a] Department

11、of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India E-mail: kns@pu.ac.in http://chemistry.puchd.ac.in/ Supporting information for this article is available on the WWW und

12、er http://dx.doi.org/10.1002/ejoc.201301248.© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Org. Chem. 2013, 7688–7692 7688carbon by using aqueous tert-butyl hydroperoxide and 4 Å molecular sieves

13、 and the coupled products, selenocarb- amates, were obtained in moderate-to-good yields.Selenocarbamates, a group of organoselenium com- pounds, act as precursors for α-alkylidene-β/δ-lactams ex- hibiting antibiotic prop

14、erties.[9] The antiviral effects of com- pounds containing this framework have also been studied.[10] N-Substituted Se-phenylselenocarbamates are useful precursors for the generation of carbamoyl radicals and other synth

15、etic transformations.[11] Selenocarbamates can be used as protected selenols and smoothly deprotected under alkaline conditions.[12] Traditionally, selenocarb- amates have been prepared from aromatic isocyanates and halo

16、alkanes by using LiAlHSeH as a selenating agent[12b]or from aryl halides by lithium/halogen exchange followed by selenium metal insertion and quenching with N,N-dialk- ylcarbamoyl chloride.[12b,12c]Dimethylformamide is n

17、ormally used as a solvent,[13] but is also considered as a source of CO, Me2N, Me2NCO and oxygen.[14] However, the direct C–H activation of form- amides has also been reported.[15–18] In these oxidative reac- tions, hydr

18、ogen abstraction can occur from two different sites: the formyl C–H or the C–H α to the nitrogen atom. tert-Butyl hydroperoxide (TBHP)/Cu-mediated direct amid- ation of β-keto esters and β-dicarbonyl phenols with form- a

19、mides has recently been achieved and occurs at the C–H centre of the formyl moiety.[16] The metal-free reaction of formamides with phthalimides and decarboxylative C–H acyloxylation of DMF have been reported to occur reg

20、iose- lectively at the C–H centre α to the nitrogen atom.[18] Xiang and co-workers reported that in the direct oxidative thiol- ation of DMF with diphenyl disulfide, the products corre- sponding to hydrogen abstraction f

21、rom the formyl C–H and the C–H α to the nitrogen atom are formed in approxi- mately equal amounts.[18a] However, by using thiophenol as a coupling partner along with Cu(OAc)2/TBHP, the re- gioselective formation of thioc

22、arbamate was observed.[18b]It may be noted that the reaction of simple phenol with DMF in the presence of CuCl/TBHP resulted in no product formation.[16b]P. Singh, A. Batra, P. Singh, A. Kaur, K. N. Singh SHORT COMMUNICA

23、TIONTable 3. Study of the substrate scope in the coupling reaction be- tween formamides and deselenides.[a][a] Reaction conditions: 1 (80 equiv.), 2 (1 equiv.), 4 Å MS (0.1 g/ 0.2 mmol), aq. TBHP (4 equiv.). [b] Iso

24、lated yield. [c] No reaction.www.eurjoc.org © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Org. Chem. 2013, 7688–7692 7690amides, namely N,N-dimethyl-, N,N-diethyl-, N,N-dibutyl- and N,N-diisopropylfo

25、rmamide (1a–1d), reacted with the diaryl diselenides to give the coupled products in moderate- to-good yields (Table 2). Diselenides bearing electron-do- nating groups on the phenyl ring (2b, 2c) smoothly afforded the co

26、rresponding coupled products 3e–3l (Table 2, en- tries 5–12). Di-1-naphthyl diselenide (2d) also gave the products 3m–3o in good yields (Table 2, entries 13–15). However, bis(2-methoxy-1-naphthyl) diselenide (2e) gave lo

27、wer yields (Table 2, entries 16 and 17), which may be due to steric factors. The use of dibenzyl diselenide (2f) as a coupling partner also gave the products 3r and 3s in yields of 74 and 67%, respectively (Table 2, entr

28、ies 18 and 19). In addition, no other new products were detected in these re- actions. To test the generality of this procedure, we also evaluated the reaction with cyclic formamides 1e–1g. The correspond- ing selenocarb

29、amates were obtained in yields of 51–71% (Table 3, entries 1–6). However, N-methylformamide (1h) and N-phenylformamide (1i) failed to give the coupled product (Table 3, entries 7 and 8). In addition, N,N-dimeth- ylacetam

30、ide (1j) also failed to react (Table 3, entry 9). Therefore it can be inferred that the product corresponding to C–H abstraction α to the nitrogen atom is not formed even when formyl C–H abstraction is blocked. It was pr

31、oposed earlier that the reaction of formamide with different coupling partners such as azole, β-keto esters and thiol in the presence of oxidants like TBHP and DTBP occurs regioselectively by formyl hydrogen abstraction

32、and proceeds through a radical pathway.[16–18] In this case also, when the radical scavenger TEMPO (4 equiv.) was added to the reaction mixture of 1a and 2a under the optimized reac- tion conditions (Table 1, entry 2), t

33、he yield of product 3a was reduced dramatically (7%), which suggests the involve- ment of a radicaloid species. Therefore we have proposed a plausible mechanism for this reaction (Scheme 2). Hydro- gen radical abstractio

34、n from formamide 1a by TBHP gives intermediate A, which reacts with PhSeSePh to give the coupled product 3a and selenyl radical B. The intermediate B either reacts with 1a to give PhSeH and intermediate A or it directly

35、reacts with the initially formed intermediate A to give the desired product. In the presence of TBHP, PhSeH is oxidized to PhSeSePh to complete the cycle.[20]Scheme 2. Tentative mechanism for the coupling reaction betwee