Chiral Cobalt(II) Complex Catalyzed Asymmetric [2,3]-Sigmatropic Rearrangement of Allylic Selenides with ?-Diazo Pyrazoleamides

Open AccessCCS ChemistryCOMMUNICATION1 Apr 2021Chiral Cobalt(II) Complex Catalyzed Asymmetric [2,3]-Sigmatropic Rearrangement of Allylic Selenides with ?-Diazo Pyrazoleamides Xiaobin Lin, Zheng Tan, Wenkun Yang, Wei Xiaohua Liu and Xiaoming Feng Lin Key Laboratory Green Chemistry Technology, Ministry Education, College Chemistry, Sichuan University, Chengdu 610064. Google Scholar More articles by this author , Tan Yang *Corresponding authors: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.020.202000345 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail Organoselenium compounds, due their high structural diversity, special function, biological activities, have drawn attention in synthetic chemistry. Herein, a novel example chiral N,N?-dioxide/cobalt(II) complex catalyzed asymmetric [2,3]-sigmatropic rearrangement allylic selenides ?-diazo pyrazoleamides is disclosed, which represents highly efficient approach optically active bearing quaternary C–Se stereocenter. Most the reactions proceed 0.5–2 mol % catalyst loading an inert-free gas atmosphere, wealth are obtained up 99% yield 97% enantiomeric excess (ee). The control experiments demonstrate reactivity selenides, as well conspicuous superiority N,N?-dioxide ligand pyrazoleamide rearrangement. mechanism studies reveal that key selenium ylides transfer chirality from stable carbon product. A feasible catalytic cycle proposed well. Download figure PowerPoint Introduction compounds emerged powerful reagents, intermediates, even catalysts organic synthesis.1–14 For instance, significant achievements catalysis been made Yeung’s15,16 Zhao’s group17–22 recently. Moreover, plethora organoselenium much medicinal domain distinctive activities.9,12 Despite great efforts devoted construction stereocenters starting materials,1–8,15–22 enantioselective route less known investigated.23–30 methods appealing terms versatile interesting stereochemistry during process. ?-selenenylation aldehydes ?-keto esters reported use electrophilic sources (Scheme 1a).24–28 kinetic resolution selenocarbonates via palladium-catalyzed decarboxylative coupling provide was achieved 1b).29 Recently, hydroselenation heterobicyclic alkenes developed afford selenol-incorporated adducts.30 Scheme 1. | (a–c) Examples chalcogen allows carbon–carbon formation.31–35 example, Doyle–Kirmse reaction sulfonium ylides, various catalysts, including high-profile copper(I) dirhodium(II) complexes, our N,N?-dioxide/nickel(II) complex, has studied recent years.36–49 In principle, arrangement similar sulfur analogs, discrimination heterotopic lone pairs on nucleophiles, stereogenic center at crucial newly formed bond rearrangement.49 Although electronegativity radii, contrast, stereoselective remains quite limited since seminal work Nishibayashi et al. 1995.36,50 relation energies, carbon–selenium weaker than carbon–sulfur bond, stability related enhances difficulties selenides.1 group demonstrated that, combination type pyrazoleamide, three types rearrangements could be efficiently enantioselectively.49,51–58 system shows excellent stereocontrol for We conjectured whether stereocenter introduction into 1c). Surprisingly, it later found N,N?-dioxide–cobalt(II) appropriate most previous cases, metal Rh2, Cu, Ir, Fe complexes favored carbene formation,36–48,59–63 but Co(II) unique cyclopropanation carbonyl others, disclosed metalloradical Dzik al.64 Lu al.65 we report generated pyrazoleamides. potentiality cobalt(II) ylide formation developed. Various were decent yields enantioselectivities. Experimental Methods dry volumetric flask (2.0 mL) charged N,N? -dioxide (0.02 mmol) mmol). Then tetrahydrofuran (THF; 2.0 added mixture stirred room temperature more 2 h before use. solution (50–500 ?L, 0.5–5 %) transferred test tube according each THF removed vacuum. Subsequently, CH2Cl2 (1.0 mL), selenide (0.1–0.15 mmol, 1.0–1.5 equiv), diazo compound 1 or 4 (0.1 1.0 equiv) successively corresponding temperature. After consumed [detected thin-layer chromatography (TLC)], residue purified column silica gel product (Pet/EtOAc = 80/1–50/1 eluent). racemic products prepared race -L2-PiPr2/Ni(OTf)2 catalyst. purification processes same those products. Results Discussion Initially, selected vinyl-substituted 1aa allyl(phenyl)selane 2a suitable substrates. L2-PiPr2, NiCl2, AgNTf2 used catalyst, best one sulfides study (Table 1, entry 1).49 desired 3aa given 84% (ee) within 5 min. No obvious effect enantioselectivity observed when silver(I) salts examined ( Supporting Information Table S1). switched optimize Ni(OTf)2 ligands derived different amino acids anilines S2, entries 2–4). finished 10 min, affording rearranged good yields. Notably, two alkoxy substituents motifs offers additional dimension diversification fine-tuning. L2-Pi(O i Pr)2, 2,6-isopropoxy groups amide unit, exhibited (2 yield) (94% ee, 4). Then, embarked screening using Pr)2 ligand. Unexpectedly, salts, Co(ClO4)2·6H2O, Co(BF4)2·6H2O, Co(OTf)2, showed better performance nickel yielding 89% ee regardless counterion cobalt (entries 5–7). Additionally, there ligand-accelerating because only 31% detected 40 min without any Naturally, settled Co(BF4)2·6H2O/ complex,b optimal investigate other parameters, such additives, concentration, no results Tables S3–S5). It worth noting Lewis acids, Ca(OTf)2, Mg(OTf)2, Al(OTf)3, Zn(OTf)2, proved ineffective transformation S3, 10–13). To delight, completed 3 low 0.5 loading, delivering final almost unchanged (89% 96% ee; 8). Further reduction 0.1 resulted drastic loss (entry 9). turned condition between phenyl-substituted 4a S6–S8). Co(OTf)2/ L3-PiPr2 complexc view enantioselectivity, 5aa 87% after 10). Optimization Rearrangements Selenium Ylidesa Entry Metal Salt(s) (mol Ligand Time Yield (%)b (%)c 1d NiCl2 (5), (10) L2-PiPr2 <5 84 L2-PiEt2 <10 73 94 L2-Pi(OMe)2 76 93 Pr) 83 Co(OTf)2 89 97 6 Co(BF4)2·6H2O 7 Co(ClO4)2·6H2O 8 (0.5) 96 9 (0.1) — 10e (2) 87 aUnless otherwise noted, carried out mmol), 1a salt/ (1?1, 0.1–10 %), M) °C. bIsolated cDetermined high-performance liquid (HPLC) stationary phase. d (1.15 equiv). eThe 35 With conditions hand, first investigated variations pyrazoleamides, keeping partner. As depicted 2, wide range substrates transformation. Among them, 1a– 1j) electron-donating electron-withdrawing substituent positions phenyl tolerated well, expected 3aa– 3ja) (83–96%) enantioselectivities (94–97% ee). all presence substrates, fused 2-naphthyl 1k), 2-furyl 1l), 3-thienyl 1m) groups, also readily converted smoothly system, targeted 3ka– 3ma) 86–96% Substrates longer shorter conjugated 1n 1o) conducted (93% 3na; 95% 3oa). Diphenylvinyl-substituted 1p, sterically demanding, provided 3pa quantitative significantly reduced (74% Substrate Scope Vinyl-Substituted Pyrazoleamidesa Isolated values determined HPLC b (1.5 aryl-substituted evaluated 3). meta- para-positions 5ba– 5ga) 76–94% 80–91% 2–8). Comparatively, containing electron-deficient aryl gave slightly higher electron-rich nonsubstituted group, time required 4b– 4f vs 4g). Furthermore, ?-(2-naphthyl)diazo 4g deliver 5ga 76% 85% disappointment, 4i ortho-substituent not compatible (<10% yield, 10), might steric hindrance date, access ?-alkyl-substituted although tried. Aryl-Substituted Ar (h) C6H5 4a) 5aa) 3-FC6H4 4b) 16 5ba) 88 3-ClC6H4 4c) 12 5ca) 91 3-BrC6H4 4d) 5da) 90 4-ClC6H4 4e) 86 5ea) 82 4-IC6H4 4f) 85 5fa) 4-MeC6H4 4g) 1.5 79 80 2-Naphthyl 4h) 5ha) 2-ClC6H4 4i) 72 Trace 5ia) – Whereafter, evaluated, partner When R arylvinyl varied, chloride methyl transformed 6ab– 6af) enantioselectivity. comparison, larger amount lower group. disubstituted 6ag), 1-naphthyl 6ah), 6ai) 15 91–95% 96–97% ee. However, 10% 6aj) allyl(benzyl)selane 2j tested under conditions, unidentified byproducts inseparable mixture. particularly noteworthy cinnamyl(phenyl)selane 2k L2-Pi(OPh)2 6ak afforded 73% greater 95?5 dr, 92% major diastereoisomer. stereoselectivity ?-diazoesters complex.44,46 Selenidesa (1.2 evaluate potential gram-scale 4d 2a). Upon treatment 3.0 mmol equivalence (1.30 g) eq. 1). performed giving 4da (1.39 90% 2). cases [2,3]-? air atmosphere inert protection, selenium-containing molecules sometimes sensitive toward oxidant light. allyl(phenyl)sulfane 9a critical 10a connection L-proline-derived L3-PrPr2. 2. (a b) Gram-scale experiments. Next, compared sulfide 9a. equivalent subjected identified systems eqs. 5), exceeded sulfur-containing 11a), albeit ratio varied ligands, salts. suggested possessed rearrangement, energy form bond. declared racemization pyramidal inversion sluggish comparison ylides,66 manifests diverse enantio-determining factors these rearrangements. Noteworthily, symmetric diallylselane 2l react 6), 6al racemates. This result diallylsulfane study.49 current atom critical. gain insight N,N?-dioxide-cobalt(II) series (see details). First, coordinated (S)- BOX BINAP, applied 2a, (<10%) 6% cases. over reactions. 5). pyrroleamide 7a proceed, accompanied decomposition 5, necessity pyrazole intermediate. diazoester 1z negative, trace unit affected both 4–7). 3,5-methyl 1w) Both dropped 3-methyl unsubstituted pyrozole units introduced 1x 1y; 7). 13C NMR spectra chemical shifts diazo-unit-attached changed dramatically, high-field shift instead ester (around 66 77 ppm). Note diphenyldiazomethane 62.6 ppm.68 indicates nucleophilic diazoester, its intermediate aryldiazoalkanes, carbenoid enhanced flanked acceptor (pyrazoleamide) donor (vinyl group).69 Thus easier nickel(II) cobalt(II), leading diazoesters system. Effect Acceptor Group Carbonyl Compoundsa PG C=N2? (ppm) 8a) 67.2 OEt 1z) 3az) 77.367 3d 3aa) 65.9 3aw) 66.1 30 75 3ax) 81 65.4 50 68 3ay) 33 65.6 dCoCl2/AgNTf2/ (1?2?1 %). addition, affect characteristic donor–acceptor upon classical carbenoids.70 On hindered pyrazoamide will increase interaction nucleophile, discriminating lone-pair electrons Se S. ready coordination ability functional enables quick ion species dipolar transition state, accelerating vinyl typical Sc(OTf)3, B(C6F5)3,71 led details), thus ruled acid accelerated dinitrogen-extrusion X-ray diffraction structures Pr)2b Co(ClO4)2·6H2O/ L3-PiPr2c indicate coordinates Co2+ octahedral 19-electon structure, structure Ni(BF4)2·6H2O/ others.49 Apart outer-shell electronic configurations ionic radii Ni(II) ions, exhibit slight changes. Based analysis Co(II)/ Ni(II)/ complexes72 length O-metal bonds little follows: ON–Co (2.01 Å) versus ON–Ni (1.98 Å); OC–Co (2.10 OC–Ni (2.03 Å). At time, N–O (1.38–1.39 (1.40–1.41 means pocket around complex. electrophilicity account improved reactivity. findings, shown 3. catalyzes N2 extrusion generate species, infrared absorption measurements Section 6.6). environment attack pair species. result, formed, followed concerted Se* center, Proposed cycle. Conclusion delineated ylides. proceeded through initiated carbenes selenides. can (up ee) operationally expedient mild conditions. examples (0.5–2 Exploring manifested difference enantioselection. involves applications exploration lab. Footnotes CCDC 1972936 1a) contains supplementary crystallographic data paper. These free charge Cambridge Crystallographic Data Centre www.ccdc.cam.ac.uk/data_request/cif. 1959861 [Co(BF4)2·6H2O/ L2-Pi(OiPr)2] c 1977471 [Co(ClO4)2·6H2O/ L3-PiPr2] available. Conflict Interest There conflict interest report. Funding authors acknowledge financial support National Natural Science Foundation China (grant nos. 21625205 21772127). 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