Checked by Saul C. Cherkofsky and Richard E. Benson.
1. Procedure
B.
erythro-3-Methanesulfonyloxy-2-butyl cyclobutanecarboxylate. A
500-ml., round-bottomed flask, cooled in an ice-water bath, equipped with a
50-ml. dropping funnel and a magnetic stirring bar is charged with
35.3 g. (0.210 mole) of erytho-2,3-butanediol monomesylate and
150 ml. of dry pyridine. Stirring is begun, and
23.7 g. (0.200 mole) of cyclobutanecarboxylic acid chloride (Note
6) is added over a period of 1 hour. The cooling bath is removed, and stirring is continued for 8 hours. The mixture is added to
500 ml. of ether, and the resulting solution washed with three
250-ml. portions of 3 N sulfuric acid. The
pyridine-free solution is washed with
250 ml. of a saturated sodium hydrogen carbonate solution and then with 250 ml. of water. The
ether solution is dried over
2 g. of anhydrous magnesium sulfate. The solvent is removed with a rotary evaporator at 25°, giving
45.1–48.0 g. (
90–96%) of
erythro-3-methanesulfonyloxy-2-butyl cyclobutanecarboxylate as a pale yellow, viscous liquid (Note
7).
2. Notes
1.
Methanesulfonic acid was obtained from Aldrich Chemical Company, Inc., and distilled prior to use. The fraction collected at 140° (0.2 mm.) was used.
2.
trans-2-Butene oxide was prepared by appropriate modification of the procedure in
Org. Synth., Coll. Vol. 4, 860 (1963). A
2-l., four-necked, round-bottomed flask fitted with a mechanical stirrer, a 1-l. dropping funnel, an
acetone–dry ice condenser, and a
thermometer is charged with
1 l. of 1,1,2,2-tetrachloroethane. The condenser is packed with dry ice and
acetone, and the flask is cooled in a
methanol-ice bath to −15°.
trans-2-Butene (153 g., 2.73 moles) (Phillips Petroleum Company, 99%) is distilled into the flask from a tared, chilled
trap. Six hundred milliliters of
40% peracetic acid (FMC Corporation), to which has been added
30 g. sodium acetate to neutralize the
sulfuric acid present, is added to the stirred solution from the dropping funnel over a period of 2 hours. The mixture is stirred at −15° for another hour, then allowed to warm to room temperature. The mixture is poured into 1 l. of ice-cold water. The organic layer is separated, washed first with
10% sodium carbonate solution, then with water, dried over
magnesium sulfate, and filtered. Distillation of the filtrate through a
75-cm. spinning-band column gives
133 g. (
68%) of
trans-2-butene oxide as a colorless oil, b.p.
52.5–55°.
3. A slight excess of
trans-2-butene oxide is used to assure complete utilization of
methanesulfonic acid. The checkers' experiments indicated that a 15% excess of the epoxide substantially reduced the amount of unreacted methane–sulfonic acid present in the product and did not appear to interfere with the succeeding steps of this procedure.
4. This order of addition and dilution is required to avoid dimerization or polymerization of the epoxide.
5. No attempt was made to purify this compound further. It had a very characteristic
1H NMR spectrum (CDCl
3, external tetramethylsilane reference): δ 1.22 (d,
J = 7.5 Hz., 3H), 1.37 (d,
J = 7.5 Hz., 3H), 3.1 (s, 3H), 3.4 (s, O
H, position variable), 4.0 (d of q,
J = 4.0, 7.5 Hz., 1H), and 4.78 (d of q,
J = 4.0, 7.5 Hz., 1H). A sample stored for several weeks at room temperature showed no change in its spectrum.
7. The
1H NMR spectrum (CDCl
3, external tetramethylsilane reference): δ 1.27 (d,
J = 6.5 Hz., 3H), 1.41 (d,
J = 6.5 Hz., 3H), 2.18 (m, 6H), 3.10 (s, 3H), superimposed on 3.2 (m, 1H)k, and 5.0 (m, 2H). IR (CDCl
3): 1725 cm.
−1.
8. Commercial material from Matheson, Coleman and Bell and recrystallized reagent gave comparable results. The yield is decreased by use of less than
1 mole of sodium borohydride per mole of
mesylate.
9. Either purified
pentane or Spectranalyzed
pentane available from Fisher Scientific Company was used.
10. The submitter reports yields of
10–11 g. (
64–71%). The checker obtained the
dioxolane in
57% yield on conducting the experiment on a sixfold scale.
11. The
1H NMR spectrum (neat, external tetramethylsilane reference) δ 1.1 (two overlapping d,
J = 6 Hz., 6H), 1.7–2.0 (m, 6H), 2.1–2.6 (m, 1H), 3.2–3.8 (m, 2H), and 4.94 (d,
J = 5 Hz., 1H).
12. This proportion of water to
N,N-dimethylformamide is needed to assure solubility (hence facile reaction) of the
acetal on heating at reflux.
13. The
1H NMR spectrum (neat, external tetramethylsilane reference): δ 1.4–2.4 (m, 6H), 2.6–3.2 (m, 1H), and 9.8 (d,
J ≈ 1.5 Hz., 1H); IR (CCl
4); 1730 cm.
−1 (C=O).
3. Discussion
Methods now available for the reduction of carboxylic acid derivatives to aldehydes require careful control of conditions to avoid overreduction or underreduction. The procedure described here is particularly convenient in that the acetal, not subject to further reduction, is formed directly in the reducing medium.
The scope of the reaction is indicated in Table I. An interesting aspect of the reaction is that the rate of the borohydride reduction step appears to be relatively insensitive to the substitutent R. It is suggested that the reaction occurs with formation of an intermediate acyloxonium ion, which is rapidly converted to acetal by reaction with the borohydride ion.
Pyridine–
borane has been shown to be the other product of this reaction; yield studies also indicate that only one hydride per borohydride ion is used efficiently in the formation of acetal.
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