Organic Reactions Volume 4 - Sciencemadness Dot Org

DIENE SYNTHESIS II 63
The configuration of VII was established by its conversion to the lactone
(VIIA) by aqueous sulfuric acid. 1
Formation of Structurally Isomeric Adducts. Two structural isomers
are possible when an unsymmetrical diene and an unsymmetrical dieno-
phile interact. Unfortunately the structures of the adducts have been
rigidly established in only seven instances: acrolein + 1-phenylbutadiene,
acrolein and methyl 3,4-dihydro-l-naphthoate + 2-ethoxy- and
2-methoxy-butadiene, 2,6-dimethoxy-4-n-amylcinnamic acid + isoprene,
and derivatives of sorbic acid + acrylyl chloride and vinyl phenyl ketone.
Acrolein and 1-phenylbutadiene give IX, as shown by conversion
of the adduct through a number of steps to o-phenylbenzoic acid. 2
U
H3C1
CO2H
lf^CHO KO fT^ N |
JcHO
CH30(f^1OCH3
CfiHn(n)
IX X XI
2-Methoxybutadiene (and 2-ethoxybutadiene) with acrolein give rise
to a single product, X. On the other hand, 2,6-dimethoxy-4-n-amylcinnamic
acid and isoprene, when heated, usually yield XI, although
in a single experiment that could not be duplicated the isomeric adduct
was formed. The principal product formed from acrylyl chloride and
derivatives of sorbic acid is XII (79%), as established by conversion
to 4-methylisophthalic acid. The orientation of ethyl sorbate and vinyl
phenyl ketone, before reaction, must be just the reverse of the previous
1 Alder, Stein, Liebmaim, and Rolland, Ann., 514, 197 (1934).
2 Lehmann and Paasche, Ber., 68, 1146 (1935).