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DOI: 10.1055/s-0030-1258992
Gold-Catalyzed Diastereoselective Synthesis of α-Fluoroenones from Propargyl Acetates
Publikationsverlauf
Publikationsdatum:
08. Oktober 2010 (online)
Abstract
A diastereoselective preparation of α-fluoroenones from propargyl acetates has been developed proceeding via a gold-catalyzed rearrangement-fluorination cascade. Control reactions are consistent with a mechanism involving a gold-mediated 3,3-sigmatropic shift followed by a direct, nongold-catalyzed electrophilic fluorination of the allenyl acetate intermediate.
Key words
gold - fluorine - catalysis - diastereoselectivity - rearrangement
- Supporting Information for this article is available online:
- Supporting Information (PDF)
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References and Notes
New address: A. D. Gee, Division of Imaging Sciences, School of Medicine, King’s College London, The Rayne Institute, 4th Floor Lambeth Wing, St Thomas’ Hospital, Lambeth Palace Rd., London, SE1 7EH, UK.
14Compounds (E)-2a and (Z)-2a were stable towards isomerization under the reaction conditions implying that the observed diastereoselectivity is under kinetic control.
15
General Procedure
for Rearrangement-Fluorination Process
Selectfluor
(2 equiv), SIPrAuCl (5 mol%), and silver trifluoromethanesulfonate
(12.5 mol%) were added to a solution of the propargyl acetate
(1 equiv) in MeCN (0.05 M). The mixture was stirred at r.t. or 40 ˚C
until TLC showed consumption of the propargyl acetate (1.5-72
h). H2O was added, and the mixture was extracted with
EtOAc (3×). The combined organic fractions were washed
with brine, dried with anhyd MgSO4, filtered, and the
solvents removed in vacuo. The crude mixture was purified by column
chromatography on silica gel.
Preparation
of 2a
The general procedure was followed using 1a (500 mg, 1.94 mmol), Selectfluor (1.37
g, 3.87 mmol), SIPrAuCl (60 mg, 0.10 mmol), and AgOTf (62 mg, 0.24
mmol) in MeCN (39 mL). The reaction was stirred for 48 h at r.t. ¹9F
NMR analysis on the crude reaction mixture indicated an E/Z ratio of
12.5:1. Purification by column chromatography on silica gel (hexane-Et2O = 20:1)
afforded the product (E)-2a as
a yellow oil (290 mg, yield 64%) as well as (Z)-2a as a yellow solid
(24 mg, yield 6%).
(
E
)-2-Fluoro-1-phenylnon-1-en-3-one [(
E
)-2a]
R
f
= 0.50
(hexane-Et2O = 9:1). ¹H
NMR (400 MHz, CDCl3): δ = 7.60-7.64
(m, 2 H), 7.35-7.40 (m, 3 H), 6.70 (d, 1 H, J = 25.3 Hz),
2.65 (dt, 2 H, J = 7.1,
3.5 Hz), 1.63 (tt, 2 H, J = 7.3,
7.1 Hz), 1.27-1.36 (m, 6 H), 0.90 (dd, 3 H, J = 6.8, 6.5
Hz). ¹³C NMR (101 MHz, CDCl3): δ = 195.6
(d, J = 38 Hz),
153.1 (d, J = 258
Hz), 130.9 (d, J = 10
Hz), 130.0 (d, J = 2
Hz), 129.2, 128.2, 119.7 (d, J = 27
Hz), 40.2 (d, J = 2 Hz),
31.6, 28.8, 23.2 (d, J = 2
Hz), 22.5, 14.0. ¹9F NMR (377 MHz, CDCl3): δ = -114.9
(dt, J = 25,
4 Hz). IR (neat): 1708 (C = O). HRMS
(ESI+): m/z calcd
for C15H19FNaO+ [M + Na]+:
257.1314; found: 257.1312.
(
Z
)-2-Fluoro-1-phenylnon-1-en-3-one [(
Z
)-2a]
Mp 30 ˚C.
R
f
= 0.42 (hexane-Et2O = 9:1). ¹H
NMR (400 MHz, CDCl3): δ = 7.66-7.70
(m, 2 H), 7.38-7.44 (m, 3 H), 6.83 (d, 1 H, J = 36.9 Hz),
2.74 (dt, 2 H, J = 7.3,
2.3 Hz), 1.69 (tt, 2 H, J = 7.5,
7.3 Hz), 1.27-1.41 (m, 6 H), 0.91 (dd, 3 H, J = 7.0, 6.8
Hz). ¹³C NMR (101 MHz, CDCl3): δ = 195.1
(d, J = 32
Hz), 154.1 (d, J = 272
Hz), 131.2 (d, J = 4 Hz),
130.6 (d, J = 9
Hz), 129.7 (d, J = 3
Hz), 128.8, 114.9 (d, J = 6
Hz), 38.0, 31.6, 28.8, 23.5 (d, J = 2
Hz), 22.5, 14.0. ¹9F NMR (377 MHz, CDCl3): δ = -125.0
(d, J = 37
Hz). IR (CH2Cl2): 1697 (C = O).
HRMS (FI+): m/z calcd
for C15H19FO [M]+:
234.1420; found: 234.1414.
Allenyl acetate 4l was
isolated as the only acetylated product during the attempted preparation
of the corresponding propargyl acetate 1l according
to the procedure of ref. 11a. This compound is presumably formed
via a spontaneous
3,3-sigmatropic rearrangement of 1l.