[1712-36-3] · C7H8O4 · Dimethyl 2,3-Pentadienedioate · (MW 156.15)
(reactive in Diels-Alder cycloadditions that yield homophthalate diesters1 and six-membered heterocycles,2 in dipolar cycloadditions that yield five-membered heterocycles,3 and in tandem conjugate addition-cyclization reactions to yield various heterocyclic systems4)
Alternate Name: 1,3-dimethoxycarbonylallene.
Physical Data: bp 58 °C/0.02 mmHg.
Solubility: sol THF, benzene, acetonitrile, DME, MeOH.
Analysis of Reagent Purity: 1H NMR (CDCl3) d 3.81 (s, 6H), 6.10 (s, 2H). IR (film) cm-1 1970, 1720, 1440.
Preparative Methods: although not commercially available, dimethyl 2,3-pentadienedioate can be prepared by the route outlined in eq 15 to give approximately 13 g of the reagent per run.
Purification: vacuum distillation.
Handling, Storage, and Precautions: dimethyl 2,3-pentadienedioate (1) polymerizes during distillation, necessitating that purification by this method be carried out in small batches. Upon standing, even overnight at refrigerator temperature, (1) becomes yellow and then orange and viscous. Preparation of amounts of (1) that will be immediately consumed, or storage of the vinyl chloride precursor and conversion to (1) as needed, appear to be warranted. This reagent should be handled in a fume hood.
By reaction with suitable dienes, especially reactive oxygenated examples, and subsequent aromatization, (1) serves as a building block for the synthesis of substituted homophthalate esters. In the example shown (eq 2),1a aromatization occurs by loss of methanol from the primary cycloadduct.
Alternatively, loss of carbon dioxide (eq 3)6 or ethylene7 from appropriate primary cycloadducts give homophthalate esters.
Reagent (1) has been shown to engage certain heterodienes2,8 in [4 + 2] cycloadditions to yield six-membered heterocyclic systems (eq 4).
Reagent (1) also enters into dipolar cycloadditions, examples involving nitrones (eq 5)3a and azides3b being well documented.
A number of applications of this reagent in transformations that are best characterized as tandem conjugate addition-cyclization reactions have been reported. These processes may combine conjugate addition of a carbon nucleophile with acylation of a heteroatom, as in eq 6,4a or conjugate addition of a heteroatom and acylation at carbon, as in eq 7.4b However, most often, heteroatoms play both nucleophilic roles (eqs 8 and 9).4c-e
Alternatively, heteroatom conjugate additions in tandem with aldol (eq 10)8 and Dieckmann (eq 11)4c condensations allow (1) to give rise to heterocyclic structures in which both reagent-derived carboxyl groups appear as substituents.
Charles S. Swindell
Bryn Mawr College, PA, USA