Chemistry of Vitamin A. XXVI. The Condensation of Aldehydes with Methyl β-Methylglutaconate¹

2-Methyl-(1Z,3E)-butadiene-1,3,4-tricarboxylic Acid, “Isoprenetricarboxylic Acid”

“…Mp: 186−192° dec. NE C 13 H 12 O 4 : 117.9 (calcd 116.1). UV (dilute NaOH): ∼215 m (ε 17 600), 274 m (ε 17 400) [lit . UV 276 (ε 17 600)].…”

“…Thus, the C 1 proton is differentiated from the C 4 proton by the presence of allylic coupling to the methyl group in the latter, and its chemical shift at δ 6.61 in both the acid and its methyl ester suggests that it is deshielded by the adjacent cis carboxyl at C 2 in the 1 E conformation . As expected for the 3 Z conformation, the C 2 methyl group does not appear to be similarly deshielded at δ 2.05, but the chemical shift range available in ref is too wide to be convincing. Similarly, allylic coupling constants between the H and CH 3 groups were found to be virtually identical in that reference (1.60 Hz) …”

“…(204-215 nm ( 15 160) and 273 nm ( 20 000). 3 Similarly, Cawley working on the chemistry of vitamin A, 8 found that 2-methyl-4-phenyl-(1E,3E)-butadiene-1,3-dicarboxylic acid (14) 13 shown in its trans-dienoid form showed only trans-cinnamic acid absorption (276 nm, 17 600) rather than that expected for a phenylbutadiene. 13 This spectral difference was assigned to the steric hindrance between the o-hydrogen on the phenyl ring and the methyl group in the trans-dienoid rotamer 14, an effect that might be expected to be smaller than in the case of 13a by comparing methyl and carboxyl group sizes.…”

Synthetic Studies on Vitamin A

“…and Nelan (1,2) described the preparation of ƒÁ-arylidene-ƒÀ-methylcrotonic acids via following schema:…”

Recent Developments In The Synthesis Of Fatty Acids

“…Some examples are given below (also cf. 88,208,209,242). In some cases more or less /3,7-unsaturation is observed, as follows: cxxv Only a small amount of the a,/3-unsaturated isomer of CXXII was obtained (177).…”