Synthesis of a non-conjugated alkenone by Knoevenagel
condensation; 1-phenylpent-1-en-4-oneSyntheticPage 166 (2001)
Submitted 26th Sep 2001, published 26th Sep 2001
A contribution from the Walton Group, St Andrews
Pentane-2,4-dione (as received),
phenylacetaldehyde (as received),
piperidine (as received),
dichloromethane (as received)
zinc acetate dihydrate (as received)
Pentane-2,4-dione (10.01 g; 0.1 mol), phenylacetaldehyde (12.0 g; 0.1 mol) and piperidine (0.1 g) were stirred for 24 hours. DCM (100 cm3) was added, and the mixture washed with 5% HCl (50 cm3) and water (50 cm3), then dried and concentrated to give 3-styrylpentane-2,4-dione. Column chromatography (PE/EtOAc) gave pure product (3.80 g; 19%).
3-Styrylpentane-2,4-dione (0.80 g; 3.96 mmol) and zinc acetate dihydrate (0.02 g) were refluxed in methanol (2 cm3) for 24 hours. Bulb to bulb distillation yielded 1-phenylpent-1-en-4-one (60 oC @ 0.04 mmHg) as a pale yellow oil (0.41 g; 65%).
The procedure is very simple, and was chosen despite the poor yields as other routes involved unpleasant and expensive reagents.
The method was reported to work for a variety of substrates.
The product, unlike other non-conjugated alkenones (see [[SyntheticPage 165] ]), was stable with respect to its conjugated isomer.
1H nmr, CDCl3:
3-Styrylpentane-2,4-dione: 1.73 (6H, s), 6.42 (1H, d, J = 16.2 Hz), 6.75 (1H, d, J = 16.2 Hz), 7.26-7.45 (5H, m)
1-phenylpent-1-en-4-one: 2.24 (3H, s), 3.35 (2H, d), 6.25-6.65 (2H, m), 7.18 (5H, m)
K. Uehara, F. Kitamura, M. Tanaka, Bull. Chem. Soc. Jpn, 1976, 49, 493.
R. Verhe, N. de Kimpe, D. Courtheyn, L. de Buyck, N. Schamp, Tetrahedron, 1982, 38, 3649.
A. J. McCarroll, PhD Thesis, University of St. Andrews, 2000.
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