Tandem Rhodium-Catalysed 1,4-Addition/Intramolecular Cyclisation
FULL PAPERS
for the next step. This solid was refluxed overnight with di-
methylmethyleneimmonium iodide (Eschenmoserꢁs salt)
(2.5 equivs.) in the required alcohol. After cooling down
evaporation afforded a residue, which was dissolved in ethyl
acetate and washed with a saturated NaHCO3 aqueous solu-
tion, followed with a 10% KHSO4 aqueous solution and
brine. Drying over MgSO4 and concentration under vacuum
afforded the crude mixture which was purified by flash
column chromatography over silica gel using ethyl acetate/
petroleum ether as elution mixture (1/20 except where
specified) to give the desired 1,1’-alkene as a colourless oil.
Method B, alkenes 17–21:[16] To a solution of sodium hy-
dride (60% in mineral oil, 1.3 equivs.) in N,N-dimethylfor-
mamide (5 mL per mmol of phosphonoacetate) was slowly
added trimethyl phosphonoacetate (1 equiv.) at room tem-
perature. The mixture was stirred for 30 min at this tempera-
ture before the addition of the bromo ester (1.3 equivs.).
After 30 min stirring at room temperature, the mixture was
heated at 1008C for 16 h. After cooling down to room tem-
perature, potassium carbonate (3 equivs.) and paraformalde-
hyde (2 equivs.) were added and the mixture was heated at
1008C for 6 h. After cooling down to room temperature, the
mixture was quenched with brine and extracted with ethyl
acetate. The layers were separated and the aqueous layer
was extracted twice with ethyl acetate. The combined organ-
ic layers were washed three times with water, then with
brine, dried over MgSO4, filtered and evaporated to dryness.
The crude was purified by silica gel chromatography using
ethyl acetate/petroleum ether (1/20) as eluent.
0.75 mmol, 0.5M in tetrahydrofuran, 1.5 equiv) at room tem-
perature. The reaction mixture was stirred overnight (18 h)
at room temperature. The reaction was quenched with
brine, extracted twice with ethyl acetate and the combined
organic layers were washed with water, dried over MgSO4,
filtered, and concentrated under vacuum. The crude mixture
was then purified by silica gel chromatography using ethyl
acetate/petroleum ether (1/10) as eluent to afford the 1,4-ad-
dition product or the corresponding cyclic product.
Acknowledgements
The authors would like to thank the EPSRC for funding. The
EPSRC mass spectrometry service at the university of Wales
Swansea is also thanked for their assistance.
References
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General Procedures for the Tandem 1,4-Addition/
Cyclisation Reaction
Conditions A: The 1,1’-alkene (0.5 mmol, 1 equiv.) and phe-
nylboronic acid (2.0 mmol, 4 equivs.) were added to a solu-
tion of [RhACHTREUNG(COD)2]ACHRTE[UGN SbF6] (11.1 mg, 4 mol%) in a mixture
of tetrahydrofuran (2 mL) and water (0.2 mL). The resulting
solution was stirred for 20 h at 808C. After cooling down to
room temperature brine was added and the solution was ex-
tracted twice with ethyl acetate. The combined organic
layers were washed with water, dried over MgSO4, filtered,
and concentrated under vacuum. The crude mixture was
then purified by silica gel chromatography using ethyl ace-
tate/petroleum ether (1/10) as eluent to afford the 1,4-addi-
tion product or the corresponding cyclic product.
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Conditions B: The 1,1’-alkene (0.5 mmol, 1 equiv.) and
phenylboronic acid (2.0 mmol, 4 equivs.) were added to a so-
lution of potassium hydroxide (22.4 mg, 8 mol%) and [Rh-
ACHTREUNG(COD)2]ACHTREUNG[SbF6] (11.1 mg, 4 mol%) in tetrahydrofuran
(2 mL). The resulting solution was stirred for 20 h at 808C.
After cooling down to room temperature brine was added
and the solution was extracted twice with ethyl acetate. The
combined organic layers were washed with water, dried over
MgSO4, filtered, and concentrated under vacuum. The crude
mixture was then purified by silica gel chromatography
using ethyl acetate/petroleum ether (1/10) as eluent to
afford the 1,4-addition product or the corresponding cyclic
product.
Conditions C: To a solution of [RhClACTHER(UNG COD)]2 (2.5 mg, 1
mol%), 1,1’-alkene (0.5 mmol, 1 equiv.), chlorotrimethylsi-
lane (0.095 mL, 0.75 mmol, 1.5 equivs.) in tetrahydrofuran
(1 mL) was added the arylzinc chloride solution (1.5 mL,
Adv. Synth. Catal. 2007, 349, 432 – 440
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