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<A NAME="RG48504ST-2">2 </A> Iron-catalyzed coupling reactions between 1,1-dichloro-1-alkenes and Grignard
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<A NAME="RG48504ST-4">4 </A> Cross-coupling reactions with organostannanes:
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Exceptions to this trend appear restricted to particular classes of substrates. 1-Chloro-1-iodo-alkenes
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1,1-Dibromoalkenes bearing a suitably located carbon-carbon triple bond in the side
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Tosylation of but-3-enylamine hydrochloride, benzylamine and p -anisidine (TsCl, Et3 N, CH2 Cl2 , 0 °C to r.t.) afforded the corresponding sulfonamides 1a (58%), 1b (77%) and 1c (84%), respectively. Benzoylation of aminoacetaldehyde dimethylacetal (BzCl, Et3 N, cat. DMAP, CH2 Cl2 , 0 °C) provided the benzamide 1d (87%).
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Representative Procedure:
N
-Benzyl-
N
-[(
Z
)-2-chloro-2-phenylvinyl]-4-methylbenzenesulfonamide (7).
To a solution of the gem -dichloroenamide 3b (178 mg, 0.500 mmol) in THF (10 mL) were successively added benzeneboronic acid (98
mg, 0.80 mmol, 1.6 equiv), a 1 M aq solution of NaOH (1.50 mL, 1.50 mmol, 3 equiv)
and Pd(PPh3 )4 (29 mg, 0.025 mmol, 0.05 equiv). After 3 h at reflux, the reaction mixture was cooled
to r.t., filtered through a pad of Celite (EtOAc) and the filtrate was evaporated
under reduced pressure. The crude material was purified by flash chomatography (petroleum
ether-EtOAc, 90:10) to afford 195 mg (98%) of 7 as a white solid; mp 124 °C. IR: 1595, 1490, 1445, 1345, 1160, 1090, 1030, 915, 815,
780, 760, 740 cm-1 . 1 H NMR (300 MHz, CDCl3 ): δ = 7.76 (d, J = 8.3 Hz, 2 H), 7.37-7.24 (m, 12 H), 6.53 (s, 1 H), 4.81 (s, 2 H), 2.43 (s, 3 H).
13 C NMR (75 MHz, CDCl3 ): δ = 143.8 (s), 136.7 (s), 136.05 (s), 136.0 (s), 132.9 (s), 129.7 (d, 2 C), 129.4
(d), 128.49 (d, 3 C or 2 C), 128.47 (d, 2 C or 3 C), 128.4 (d), 127.8 (d), 127.3 (d,
2 C), 126.9 (d, 2 C), 122.9 (d), 52.2 (t), 21.6 (q). MS (EI, 70 eV): m/z (%) = 400 (1) [M(37 Cl) + H+ ], 399 (3) [M(37 Cl)+ ], 398 (2) [M(35 Cl) + H+ ], 397 (9) [M(35 Cl)+ ], 362 (1) [M - Cl+ ], 242 (4) [M - Ts+ ], 206 (5), 178 (2), 155 (2), 92 (8), 91 (100), 89 (4), 65 (7). Anal. Calcd for C22 H20 ClNO2 S: C, 66.40; H, 5.07; N, 3.52. Found: C, 66.47; H, 4.99; N, 3.48.
<A NAME="RG48504ST-13">13 </A>
In all the cross-couplings investigated, GC-MS and NMR analyses of the crude β-haloenamides
indicate a stereoisomeric ratio > 95:5.
<A NAME="RG48504ST-14E">14e </A>
The Pd-catalyzed hydrogenolysis of the gem -dibromo-enamide 13 with n -Bu3 SnH led to the (Z )-b-bromoenamide 26 (55%), whose configuration was readily assigned by 1 H NMR, and to the fully reduced enamide 27 (15%) as a by-product. However, no trace of the (E ) geometrical isomer of compound 26 could be detected. A similar hydrogenolysis of the gem -dichloroenamides could not be achieved (Scheme
[4 ]
).
Scheme 4
This result confirms that in b,b-dihaloenamides of type A , the oxidative addition of Pd(0) complexes occurs at the less-hindered carbon-halogen
bond, as in the non-hetero-substituted series. For the Pd-catalyzed hydrogenolysis
of 1,1-dibromoalkenes, see:
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Uenishi J.
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Yonemitsu O.
Tsuji J.
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Izaki Y.
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3493
<A NAME="RG48504ST-15">15 </A>
The (Z )-olefinic configuration of the β-chloroenamides of type B was further confirmed by their ability to undergo dehydrochlorination (E2 anti -elimination) by treatment with a base, whereas the (E ) geometrical isomers would not react under these conditions, see ref. 16.
<A NAME="RG48504ST-16">16 </A> Some chiral disubstituted ynamides have been synthesized from enamides by bromination
(Br2 or NBS) leading to stereomeric mixtures of β-bromoenamides, in which the (Z ) isomer was selectively converted to the desired disubstituted ynamide by treatment
with a base (t -BuOK, THF) whereas the (E ) isomer did not react; see:
Wei L.-L.
Mulder JA.
Xiong H.
Zificsak CA.
Douglas CJ.
Hsung RP.
Tetrahedron
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459
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Zificsak CA.
Mulder JA.
Hsung RP.
Rameshkumar C.
Wei L.-L.
Tetrahedron
2001,
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<A NAME="RG48504ST-18">18 </A>
Witulski B.
Gößmann M.
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1793
<A NAME="RG48504ST-19">19 </A>
Mulder JA.
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<A NAME="RG48504ST-20A">20a </A>
Frederick MO.
Mulder JA.
Tracey MR.
Hsung RP.
Huang J.
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Shen L.
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<A NAME="RG48504ST-20B">20b </A>
Dunetz JR.
Danheiser RL.
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Zhang Y.
Hsung RP.
Tracey MR.
Kurtz KCM.
Vera EL.
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<A NAME="RG48504ST-21A">21a </A>
Rodríguez D.
Castedo L.
Saá C.
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2004,
377
<A NAME="RG48504ST-21B">21b </A>
Rodríguez D.
Castedo L.
Saá C.
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783
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Frederick MO.
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<A NAME="RG48504ST-22">22 </A>
Representative Procedure:
N
-Benzyl-
N
-(2-phenylethynyl)-4-methylbenzenesulfonamide (
21).
To a solution of β-chloroenamide 7 (100 mg, 0.251 mmol) in toluene (10 mL) were successively added 50% aq NaOH (10 mL)
and tetrabutylammonium hydrogensulfate (17 mg, 0.050 mmol, 0.2 equiv) and the resulting
mixture was vigorously stirred at r.t. After 7 h, the reaction mixture was cooled
to 5 °C, and diluted with H2 O and Et2 O. The layers were separated and the aqueous phase was extracted with Et2 O. The combined extracts were washed with a sat. aq solution of NH4 Cl, brine, dried over MgSO4 , filtered and concentrated under reduced pressure. The residue was purified by flash
chromatography (petroleum ether-EtOAc, 95:5) to afford 74 mg (81%) of 21 as a pale yellow waxy solid. IR: 3060, 3030, 2235, 1595, 1490, 1445, 1420, 1355,
1160, 1050, 1030, 940, 815, 765, 690, 655 cm-1 . 1 H NMR (300 MHz, CDCl3 ): δ = 7.77 (d, J = 8.3 Hz, 2 H), 7.30-7.14 (m, 12 H), 4.55 (s, 2 H), 2.40 (s, 3 H). 13 C NMR (75 MHz, CDCl3 ): δ = 144.7 (s), 134.7 (s), 134.5 (s), 131.1 (d, 2 C), 129.8 (d, 2 C), 128.9 (d,
2 C or 3 C), 128.6 (d, 2 C), 128.2 (d, 3 C), 127.7 (d, 3 C or 2 C), 122.8 (s), 82.7
(s), 71.4 (s), 55.7 (t), 21.7 (q). MS (EI, 70 eV): m/z (%) = 361 (21) [M+ ], 207 (9), 206 (45) [M - Ts+ ], 205 (6), 179 (26), 178 (11), 165 (3), 155 (3), 105 (6), 92 (8), 91 (100), 65 (13).