[6180-21-8] · C2ClLi · Lithium Chloroacetylide · (MW 66.41)
Alternate Name: chloroethynyllithium.
Solubility: sol ether.
Preparative Method: prepared in ether solution under anhyd conditions by treatment of cis- or trans-1,2-dichloroethylene with 2 equiv Methyllithium at 0 °C under N2.2
Handling, Storage, and Precautions: dry lithium chloroacetylide is explosive (as are the other metal haloacetylides), but may be safely handled and kept in the solution in which it is prepared under N2.
Lithium chloroacetylide reacts with aldehydes and ketones in good yield to form chloroethynyl substituted carbinols (eq 1).1 -3 Alkylations, silylations, and stannylations all proceed well.1 Other electrophiles such as Carbon Dioxide and a-naphthyl isocyanate also produce the expected addition products.2
A protected tetrahydroxylactone is reported to give the monoaddition product (eq 2).4 Reaction with Methyl Chloroformate at -78 °C can be used to prepare methyl chloropropiolate (eq 3).2,5 In this reaction, explosions have occurred in more than one instance, possibly due to the formation of tris(chloroethynyl)carbinol.5,6
Lithium chloroacetylide has been used in coupling reactions. In the presence of Copper(I) Iodide, coupling to Allyl Bromide was observed (eq 4).7 When treated with cyclohexenylzinc bromide, lithium chloroacetylide gives 2-cyclohexenylacetylene (43%) and 1,1-bis(2-cyclohexenyl)ethylene (16%), in analogy to its reactions with other allylic organozinc compounds (eq 5).8
The chloroacetylides of Na, K, and Ca have also been prepared, as well as some bromo and fluoro analogs.9 All these chloroacetylides react with the organohalides of Al, Sn, Pb, As, Sb, or Bi to exchange the metal (e.g. eq 6)3,10
Suzuki et al.11 have used lithium chloroacetylide to prepare lithium 2-chloroethynyltrialkylborates, which react with Iodine to give the corresponding symmetric alkynes (eq 7).
Ieva L. Reich & Hans J. Reich
University of Wisconsin, Madison, WI, USA