Allylic Substitution Catalyzed by Xylophos-Pd
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the coexistence of several catalytically active species in a labile equilibrium. From
this point of view xylophos behaves according to expectations: its ef®ciency ranges
between the excellent one of diphosphines forming ®ve-membered chelates and the
poor one of diop analogues involving seven-membered chelates [1g].
Experimental
General
NMR spectra were recorded on a Varian Gemini 300 NMR spectrometer at 300 (1H), 75.4 (13C), and
1
121.4 (31P) MHz in CD2Cl2 in 5 mm sample tubes at 300 K. H and 13C spectra were referenced to
internal TMS, 31P chemical shifts are quoted relative to external 85% H3PO4. The numbering of
carbon and phosphorus atoms refers to that given in the formula of 10; interchangeable assignments
are marked by an asterisk.
[PdCl2(xylophos)] (10; C32H32Cl2O3P2Pd)
55.0 mg (1.05 mmol) of xylophos were added to a solution of 38.3 mg (1 mmol) of [PdCl2(PhCN)2]
in 2 cm3 of CH2Cl2. After 10 min, the product was precipitated by addition of diethyl ether; ®ltration
afforded 65 mg (91%) of 10.
1H NMR: ꢁ 1:19 (s, 3H, CH3), 1.26 (s, 3H, CH3), 2.42 (ddd, 1H, H-50, 3J(H-50, H-5) 15.8 Hz,
2
3J(H-50, H-4) 8.6 Hz, J(H-50, P-1) 5.8 Hz), 2.80 (m, 1H, H-5), 2.91 (t, 1H, H-3, 3J(H-3, H-
3
4) 2J(H-3, P-2) 6.9 Hz), 4.49 (m, 1H, H-4), 4.74 (dd, 1H, H-2, J(H-2, H-1) 4.1 Hz, 3J(H-2, P-
3
3
2) 6.9 Hz), 5.60 (dd, 1H, H-1, J(H-1, H-2) 4.1 Hz, J(H-1, P-1) 2.1 Hz), 7.30±8.20 (m, 10H,
13
Ã
Ã
CH ) ppm; C NMR: ꢁ 26:1 (C-7 ), 26.3 (C-8 ), 26.8 (dd, C-5, J(C-5, P-2) 19.5 Hz, J(C-5,
P-1) 32.5 Hz), 45.2 (dd, C-3, J(C-3, P-2) 23.9 Hz, J(C-3, P-1) 10.8 Hz), 73.3 (d, C-4, J(C-4,
P)1 4.5 Hz), 82.4 (t, C-2, J(C-2, P-2) 2.9 Hz), 103.6 (C-1), 111.8 (C-6), 124.3, 125.0, 125.2, 125.8
(Carom), 127.4±135.3 (CHarom) ppm; 31P NMR: ꢁ 18:2 (d, P-1, J(P, P) 7.4 Hz), 22.8 (d, P-2)
2
ppm; calcd.: C 54.60, H 4.58; found: C 54.47, H 4.65.
Allylic alkylations with dimethyl malonate [5]
4 cm3 of dry THF were degassed, [Pd(ꢂ3-allyl)Cl]2 (1.8 mg, 0.005 mmol, 1 mol% Pd), xylophos
(10.5 mg, 0.02 mmol, 2 mol%), and 1 mmol of substrate were added in sequence, and the solution was
stirred for 15 min. A solution of malonate anion was prepared by adding NaH dispersion (63 mg,
1.5 mmol) in portions to a degassed solution of dimethyl malonate (198 mg, 171mm3, 1.5 mmol) in
4 cm3 of THF. After 30 min, the resulting turbid solution was added via a te¯on tube to the ice-cooled
solution containing allyl acetate 2a±6a and the catalyst, and the mixture was stirred overnight at room
temperature. The reaction was quenched by addition of a small amount of 2 N HCl, and the mixture
was extracted with Et2O (3Â10 cm3). The combined extracts were washed with brine until neutral and
dried over Na2SO4. After removal of the solvent the crude products were puri®ed by column
1
chromatography (silica gel); the purity of the isolated products was checked by H NMR spectro-
scopy.
2b: Column: 10Â2.2 cm, PE:CH2Cl2 50:50; UV/Vis: ꢃmax 290 nm; ee: chiral HPLC (Chiralcel
OD-H1, 250Â4.6 mm, 2% 2-PrOH / 98% n-hexane); speci®c rotation calculated for optically pure
20
D
(S)-2b: ꢀ
22:4 (c 1.8, CHCl3) [6].
3b: Column: 25Â2.5 cm, PE:Et2O 75:25; UV/Vis: ꢃmax 220 nm; ee: enantioselective GC:
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(50% octakis-(6-O-methyl-2,3-di-O-pentyl)-ꢄ-cyclodextrin, FS, 0.25Â25 m, 0.5 atm H2, 55ꢁC); H
1
Coupling phosphorus atom not identified