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Chemoselective Transfer of Allyl Or Phenyl Group from Allyl(Phenyl)Germanes in Pd-Catalyzed Reactions with Aryl Halides

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Chemoselective Transfer of Allyl Or Phenyl Group from Allyl(Phenyl)Germanes in Pd-Catalyzed Reactions with Aryl Halides doi:10.1246/cl.2011.967 Published on the web September 5, 2011 967 Chemoselective Transfer of Allyl or Phenyl Group from Allyl(phenyl)germanes in Pd-catalyzed Reactions with Aryl Halides Jean-Philippe Pitteloud, Yong Liang, and Stanislaw F. Wnuk* Department of Chemistry and Biochemistry, Florida International University, Miami,Florida 33199, USA (Received May 27, 2011; CL-110451; E-mail: wnuk@fiu.edu) Treatment of chloro(phenyl)germanes with allylmagnesium bromide yielded allyl(phenyl)germanes. Coupling of the allyl- GeCln MgBr (n equiv) Ge n (phenyl)germanes with aryl halides in 1,4-dioxane in the presence of aqueous NaOH and Pd catalyst resulted in Heck-type transfer of 4-nEt2O 4-n ° the allyl group providing the corresponding allylated aryls. On the 0 C or r.t. i f ll l l i i 1 n = 3 (85%) other hand, react on o a y (pheny )germanes w th SbF5 nterca- 2 n = 2 (94%) lated in graphite intoluene and subsequent treatment of the 3 n = 1 (92%) resulting germanylfluorides with TBAF generates reactive hyper- PhMgBr (5 equiv) GeCl valent fluorogermanates that undergo Stille-like Pd-catalyzed 3 3 (44%) Et O cross-coupling with aryl halides in wet toluene to provide biaryls. 2 Scheme 1. Synthesisof allyl(phenyl)germanes 1­3. The application of organogermanes to Pd-catalyzed couplings 1 has thus far received much less attention than the couplings Treatment of PhGeCl3,Ph2GeCl2,orPh3GeCl with 3, 2, or 1 involving organostannanes and organosilanes.2 This is due to the equivof allylmagnesium bromide yielded stabletriallyl(phenyl)- lower reactivity of tetracoordinated organogermanium species, the germane (1), diallyl(diphenyl)germane (2), or allyl(triphenyl)ger- less developed syntheses of vinyl/aryl germanyl derivatives, and mane (3), respectively (Scheme 1). Moreover, treatment of the higher cost of germanium relative to silicon.3 allyl(trichloro)germane with phenylmagnesium bromide also Based on the available knowledge on the susceptibility of produced allyl(triphenyl)germane (3) (44%).21 organogermanes toward coupling, it appears that the coupling is Attempted coupling of triallyl(phenyl)germane (1)with aryl promoted either by: (i) intramolecular chelation of a pendant iodides employing conditions used for the reactions of triallyl- 18 Lewis basic heteroatom which renders the Ge center “permanent- (phenyl)silanes (PdCl2/TBAF/PCy3/DMSO/H2O) or vinyltris- 4­7 12 ly” pentavalent or (ii) the presence of at least one heteroatom (trimethylsilyl)germanes (NaOH/H2O/H2O2/[Pd(PPh3)4]/THF) bound to the Ge center that renders the Ge center more susceptible with ArX failed to yieldbiaryl products and resulted in the to coordination by an external Lewis basic ligand (e.g., fluoride, recovery of 1. However, treatment of 1 with 1-butyl-4-iodoben- hydroxide, etc.), thereby also rendering the Ge center penta- zene (4a) (18 h, 95 °C), under conditions employed for the 8­17 9 valent. Although the effects offluoride/base activation and Pd- coupling of trichloro(phenyl)germanes [NaOH (8 equiv)/H2O/ catalyst/ligand combination on the coupling of organogermanes dioxane/Pd(OAc)2], yielded 1-allyl-4-butylbenzene (5a) resulting are still ambiguous, all but one4 successful exampleof germane from the transfer of the allyl group (Table 1, Entry 1). The ¡- couplings with aryl/alkenyl halides involved activation with either methyl vinylisomer 6a was also formed (5a/6a;55% total, 87:13). base or fluoride. These unexpected findings prompted us to examine the effect of Recently we reported that trichloro(phenyl)-, dichloro(diphen- reaction parameters on the transfer of allyl group from germane yl)-, and chloro(triphenyl)germanes undergo Pd-catalyzed cross- precursors 1­3. couplings with aryl bromides and iodides in the presence of TBAF Thus, treatment of 1 with 4a at higher concentrations of intoluene with addition of a measured amount of water. One NaOH afforded a regioisomericmixture of 5a and 6a inhigher chloride ligand on the Ge center issufficient to allow efficient yields (Entries 2 and 3). The combination of NaOH and Pd catalyst activation by fluoride and subsequent transfer of one, two or proved to be criticalfor the transfer of allyl groups from 1,since 16,17 three phenyl groups from the organogermane precursors. We reactions with only Pd(OAc)2 yielded product 5a in much lower showed that arylchlorogermanes can render a coupling efficiency yield (Entry 4). The use of different Pd catalysts also gave comparable to that of the more established stannane and silane coupling products with similar yields and regioselectivity (Entries counterparts and that their coupling efficiency reflected their 5 and 6). Reactions employing Et3N and TBAF afforded 5a in ability to generate reactive hypervalent intermediates upon fluoride moderate yields (Entries 7 and 8). The ratioofisomers 5a/6a activation.17 seems to be independent of the reaction conditions. For example, Hiyama and co-workers utilized tri-, di-, and monoallyl(aryl)- temperature has no effect on regioselectivity of the reaction of silanes in Pd-coupling with aryl halides to access biaryls.18 They allylgermane 1 with 4a. Thus, increasing the temperature from 50 suggested that allylsilanes spontaneouslycleave upon treatment to 70 to 95 °C increased the reaction rate but the same ratioof the with TBAF and an appropriate amount of water to provide an isomeric products 5a/6a (µ90:10) was observed after 1 h at all active silicate species that promotes transmetalation. Although the temperatures and remained constant after prolonged heating. chemistry of allylgermanes iswell established,19,20 the application To further investigate the transfer of the allyl group, the of allyl organogermanes as substrates for the Pd-catalyzed cross- reactions of allylgermanes 1, 2,or3 with other aryliodides 4a­4c coupling with aryl halides has not been investigated. Herein, we (1.05 equiv) were carried out (Table 2). We found that triallyl- report chemoselective application of tri-, di-, and monoallyl- germane 1 gave higher yields of allylated aryl products 5a­5c (phenyl)germanes toward Pd-catalyzed reactions. than diallylgermane 2,which in turn were more efficient than Chem. Lett. 2011, 40, 967­969© 2011 The Chemical Society of Japan www.csj.jp/journals/chem-lett/ 968 Table1. Effect of the various reaction parameters on the efficiency of Table2. Allylation of aryliodides with allyl(phenyl)germanes 1­3a transferring allyl group from triallyl(phenyl)germane (1)a Ge n NaOH, Ar-I (4) I 4-n Pd, 1,4-dioxane Ar Ar Ge 3 Base, Pd 95 °C, 18 h 1,4-dioxane 1 n = 3 56 ° 2 n = 2 Series a Ar = 4-BuC H 95 C, 18 h 3 n = 1 6 4 Bu Bu Bu b Ar = 1-naphthyl c Ar = 4-MeOC6H4 1 4a 5a 6a i l i c ­ Y e d Rat o Base Yield Ratioc Entry Germane Ar IPd /%b,c Entry Base Pd 5:6 /equiv /%b,c 5a:6a 1 14aPd(OAc)2 78 82:18 1 NaOH 8 Pd(OAc)2 55 87:13 2 24aPd(OAc)2 47 82:18 2 NaOH 10 Pd(OAc)2 60 89:11 3 34aPd(OAc)2 32 86:14 3 NaOH 12 Pd(OAc)2 84 82:18 4 14aPd2(dba)3 80 86:14 ® 4 NaOH Pd(OAc)2 15 94:6 5 24aPd2(dba)3 55 85:15 5 NaOH 12 Pd(PPh3)4 78 84:16 6 34aPd2(dba)3 33 85:15 6 NaOH 12 Pd2(dba)3 85 86:14 7 14bPd(OAc)2 73 90:10 7Et3N 10 Pd(OAc)2 32 83:17 8 24bPd(OAc)2 51 90:10 8 TBAF 10 Pd(PPh3)4 42 82:18 9 34bPd(OAc)2 29 91:9 aCouplings were performed on 0.16 mmol scaleof 1 (0.03 M) with 10 14bPd2(dba)3 88 91:9 1.05 equivof 4a and 0.08 equivof Pd catalyst indioxane (5 mL) and 11 24bPd2(dba)3 69 92:8 agiven stoichiometric amount of NaOH (2 M) or other bases. 12 34bPd2(dba)3 40 93:7 d bOverall yieldof 5a and 6a. cDetermined by GC-MS of the crude 13 14cPd(OAc)2 90 79:21 e reaction mixture. 14 24cPd(OAc)2 37 76:24 f 15 34cPd(OAc)2 15 73:27 a li f l l f ­ ll l i f i ll l i ­ Coup ngs were per ormed on 0.16 mmo sca eo germanes 1 3 a y germane 3 n trans err ng a y groups (e.g., Entr es 1 3). The i i f l li i f f ff ­ i li l i (0.03 M) w th 1.05 equ vo ary ha des, 12 equ vo NaOH, and use o Pd2(dba)3 a orded the products 5a 5c nsght yhgher i f l b ll i l f c i l i l i i i 0.08 equ vo Pd cata yst. Overa y e do 5a and 6a. Based on y e ds, though the 5 to 6 reg ose ect v ty was not mproved (e.g., GC-MS and 1H NMR of the purified reaction mixture. dWith Entries 1­3 vs. 4­6). The bulkier 1-iodonaphthalene (4b) showed a e f [Pd2(dba)3] (56%, 81:19). With [Pd2(dba)3] (39%, 79:21). With small enhancement in the regioselectivity as compared to 4a (e.g., [Pd2(dba)3] (14%, 80:20). Entry 1 vs. 7). Transfer of the allyl group from allylgermanes also occurred efficientlywith p-MeOC6H4I(4c) (Entries 13­15) but failed with p-CF3C6H4I. I Since triallylgermane 1 could transfer up to three allyl n 4b substituents in the reaction with aryl halides, experiments with 3 Ge (3 equiv) equivof 1-iodonaphthalene (4b) were attempted.
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