[6262-42-6] · C3Cl4 · Tetrachlorocyclopropene · (MW 177.83)
Physical Data: bp 130-133 °C; d 1.450 g cm-3.
Solubility: sol common organic solvents; undergoes ring opening in H2O at 25 °C and in alcohols at 50-80 °C.5
Form Supplied in: colorless liquid; widely available.
Analysis of Reagent Purity: GC, IR.5
Preparative Method: from Sodium Trichloroacetate and Trichloroethylene.6
Handling, Storage, and Precautions: lacrymator; must be stored at 4 °C in the absence of moisture; use in a fume hood.
Tetrachlorocyclopropene (1) is widely used as an entry to cyclopropenium cation chemistry. Thus, upon treatment with Aluminum Chloride, (1) readily forms the trichlorocyclopropenium salt (2) in virtually quantitative yield,7 which can further be converted to a variety of cyclopropenium cations (3) (eq 1).2 Compound (2) has been the starting point for the synthesis of a broad variety of heterocycles, e.g. benzimidazoles or 1,5-benzodiazepines,8 2-azacalicenium salts,9 or indolizines.10
Treatment of (2) with arenes and subsequent hydrolysis with alcohols gives rise to arylpropiolates (4) in good to excellent yields (eq 2).11
The transformation of (2) to substituted cyclopropenones opens up another wide field in synthetic chemistry. For example, vinyl-substituted cyclopropenones derived from (2) have been proven to be excellent precursors to a-methylene-g-butyrolactones.12
Another important application of (2) was demonstrated with the synthesis of the dialkynyl-substituted cyclopropenone (5), which was envisaged as a precursor to new allotropic forms of carbon such as C18, C24, or C30, respectively (eq 3).13 Moreover, (5) can easily be converted to the enediyne (6),13 a structure element which plays a pivotal role in the chemistry of the esperamicin/calicheamicin class of anticancer drugs.14
Diarylcyclopropenones (7), also readily obtained from (2), can be decarbonylated to symmetrically or unsymmetrically substituted alkynes (8) in high yields (eq 4).15
Reagent (1) undergoes thermal ring opening to perchlorovinylcarbene (9), which is efficiently trapped with a large number of alkenes to form 1-chloro-1-trichlorovinylcyclopropanes (10).3 From these intermediates, ethynylcyclopropanes (11) as well as cyclopropylideneacetates (12) are readily available (eq 5), which have been widely used in natural and nonnatural product synthesis,16 including a- and b-amino acids,16d,e and b-lactams.16f
Reagent (1) can react as an electron-poor dienophile in [4 + 2] cycloadditions to yield bicyclo[4.1.0]heptene derivatives (13) (eq 6) allowing, for example, the synthesis of tropolones17 or triafulvalenes.18 The stereochemical course of such cycloadditions has been investigated.4
Oliver Reiser & Armin de Meijere
Georg-August-Universität Göttingen, Germany