Organic Syntheses, Coll. Vol. 4, p.311 (1963); Vol. 34, p.29 (1954).
In a high-pressure autoclave
, arranged for agitation by shaking or rocking, are placed 286 g. (336 ml., 4.08 moles) of crotonaldehyde
, 294 g. (5.06 moles) of methyl vinyl ether
, and 1.1 g. of hydroquinone (Note 1)
and (Note 2)
. The autoclave is heated to 200° (Note 3)
and held there for 12 hours. The autoclave is cooled and vented, and the black product is distilled through a 1 by 60 cm. helix-packed column
. The yield of 3,4-dihydro-2-methoxy-4-methyl-2H-pyran
is 270–297 g.
), b.p. 42–50° /19 mm.
1.4349–1.4374 (Note 4)
, (Note 5)
, and (Note 6)
The submitters condensed the methyl vinyl ether
in the aldehyde cooled to 0° and then charged this mixture to a precooled autoclave. The checkers cooled the autoclave containing the crotonaldehyde
to −70°, evacuated, and condensed the required amount of methyl vinyl ether
directly into the autoclave.
The autoclave should be capable of withstanding a pressure of 3000 p.s.i. This provides a margin of safety, since at 220° the pressure is about 2600 p.s.i.
The submitters used approximately three times the quantities reported here and obtained yields of 82–83%.
Under comparable conditions the submitters found that the corresponding dihydropyran derivatives were similarly obtained by the condensation of acrolein
with methyl vinyl ether
in 80–81% yield, with ethyl vinyl ether
(77–85% yield), with n-butyl vinyl ether
(82% yield), with ethyl isopropenyl ether
(50% yield), and with n-butyl cyclohexenyl ether
(40% yield). Other α,β-unsaturated carbonyl compounds that have thus been condensed with ethyl vinyl ether
(87% yield), methacrolein
(40% yield), α-ethyl-β-n-propylacrolein
(54% yield), cinnamaldehyde
(60% yield), β-furylacrolein
(85% yield), methyl vinyl ketone
(50% yield), benzalacetone
(75% yield), and benzalacetophenone
This preparation is referenced from:
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved