[17994-23-9] · C3Cl2O3 · Dichlorovinylene Carbonate · (MW 154.94)
Alternate Name: 4,5-dichloro-1,3-dioxolen-2-one.
Physical Data: mp 19 °C; bp 39-40 °C/10 mmHg.
Solubility: sol acetone, benzene, xylene.
Handling, Storage, and Precautions: lachrymator; may be stored indefinitely in the refrigerator; slowly decomposes to CO and oxalyl chloride in the liquid state or in dilute aprotic solvents; decomposes at rt with phosphorus nucleophiles.
Dichlorovinylene carbonate (1) is used primarily as a dienophile (weak) in thermal and photocycloaddition reactions. Once formed, the cycloadducts are hydrolyzed to give 1,2-dione or glyoxylic acid derivatives that are generally used as precursors of target molecules. As such, it may be considered a synthon for dicarbon suboxide (eq 1).
Benzene, anthracene, and phenanthrene derivatives undergo cycloadditions with (1) to give 1,2- or 1,4-adducts. Acetophenone is generally used as the photosensitizer.5 Typical chemistry is illustrated (eq 2) by its photocycloaddition with benzene to give adduct (2) that was then hydrolyzed to dione (3).2
Phenanthrene and (1) give predominately one stereoisomer (shown) in a [2 + 2] photoreaction. Hydrolysis to the diketone followed by a benzilic acid rearrangement gives the cyclopropyl-a-hydroxy acid (eq 3).6
With anthracene, a thermal cycloaddition (refluxing in p-xylene) gives a 1,4-adduct (84%) and its dione (78%) upon hydrolysis (eq 4; X = H).7 Ketene derivatives are available through this chemistry (eq 4; X = OMe).3
Alkenes,8 alkynes,1,9 and dienes7,10 undergo cycloaddition as well. Eq 5 shows a two-step synthesis of a cyclobutenedione derivative11 (see N,N-Diethyl-1-propynylamine for an alternate route). Less substituted alkenes such as ethylene also work well in this type of reaction.8
Cyclopentadienes give bicyclo[2.2.1]heptenediones in thermal [4 + 2] cycloadditions (eq 6),12 where intermediate adducts are usually a mixture of endo and exo products. Addition rates depend on the cyclopentadiene used. Acyclic dienes tend to add in a [2 + 2] manner.10 Other reactions include addition to norbornenes,13 annulenes,14 3-phospholenes,15 and o-benzoquinones.16
Kenneth C. Caster
Union Carbide Corporation, South Charleston, WV, USA