Organic Syntheses, CV 5, 80
α-BENZYLIDENE-γ-PHENYL-Δβ,γ-BUTENOLIDE
Submitted by Robert Filler, Edmund J. Piasek, and Hans A. Leipold
1.
Checked by S. Trofimenko and B. C. McKusick.
1. Procedure
The apparatus consists of a
200-ml., three-necked, round-bottomed flask fitted with
thermometer,
reflux condenser, and
gas-inlet tube. The flask is charged with
17.8 g. (0.10 mole) of 3-benzoylpropionic acid (Note
1),
10.6 g. (10.6 ml., 0.10 mole) of benzaldehyde,
61.3 g. (57 ml., 0.60 mole) of acetic anhydride, and
8.2 g. (0.10 mole) of powdered anhydrous sodium acetate (freshly fused). The flask is placed in an
oil bath maintained at a temperature of 95–100° and is kept there for 2 hours while dry oxygen-free
nitrogen is passed through the reaction mixture (Note
2). At the end of this time the flask is removed from the oil bath, and the hot solution is decanted from the
sodium acetate into a
250-ml. Erlenmeyer flask. The solution is kept at 0–5° in a
refrigerator for 1 hour, during which time
α-benzylidene-γ-phenyl-Δβ,γ-butenolide separates as an orange solid.
About
40 ml. of 95% ethanol is added to the contents of the flask, and the butenolide is brought into suspension by thoroughly breaking up all lumps with a
spatula. The suspension is filtered with suction, and the filter cake is washed with
30 ml. of cold 95% ethanol and then with 100 ml. of boiling water to remove any
sodium acetate present. The butenolide is obtained as a yellow solid, m.p.
149–154°, weight
11.1–12.4 g. (
45–50%), after being dried overnight in a
vacuum desiccator. This product, which is pure enough for most purposes, may be further purified by crystallization from
95% ethanol (Note
3).
2. Notes
3. About
75 ml. of ethanol is used for every gram of butenolide to be dissolved. Clarification of the solution with charcoal should be avoided because the butenolide tends to separate from solution during filtration and clogs the
steam-jacketed funnel. The crystallized butenolide melts at
150–152°.
3. Discussion
The method described above may be used for the preparation of a wide variety of butenolides substituted in the arylidene ring with either electron-withdrawing or electron-releasing substituents. γ-Lactones such as α-
benzylidene-γ-phenyl-Δβ,γ-butenolide are isoelectronic with azlactones, but have received much less attention. Like the azlactone ring, the butenolide ring may be opened readily by water, alcohols, or amines to form keto acids, keto esters, or keto amides.
9 α-Benzylidene-γ-phenyl-Δβ,γ-butenolide is smoothly isomerized by
aluminum chloride to
4-phenyl-2-naphthoic acid10 in 70% yield via intramolecular alkylation. Grignard reagents add
1,4 to the α,β-unsaturated carbonyl system, with the lactone ring remaining intact,
11 while
phenyllithium leads to ring opening and the formation of
1,1-diphenyl-2-phenacylcinnamyl alcohol.
11 The butenolide gives reduced dilactones, on treatment with
lithium aluminum hydride.
12
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