[821-10-3] · C4H4Cl2 · 1,4-Dichloro-2-butyne · (MW 122.98)
Physical Data: colorless liquid, bp 165-168 °C; d 1.258 g cm-3.
Solubility: sol most organic solvents.
Form Supplied in: neat liquid of high purity.
Preparative Method: conveniently prepared by treating 1,4-butynediol with Thionyl Chloride.1 However, as a precautionary measure the medium is diluted with CH2Cl2 and cooled to -30 °C before adding thionyl chloride to avoid hazards associated with the exothermicity of the reaction.2
Handling, Storage, and Precautions: flammable liquid, lachrymator, and irritant; use in a fume hood.
A variety of polysubstituted 1,3-butadienes are conveniently prepared by a two-step sequence involving addition-elimination (eq 1). Thus halogens/pseudohalogens,3 aryl selenosulfonates,4 and silanes5 can be added followed by reductive dehalogenation with Zinc. These functionalized butadienes can be used as dienes in cycloadditions3,6 and in the synthesis of allenes4 (eq 2). Silylbutadienes find use as adhesion promoters5 and in complexes with iron tricarbonyl undergo unprecedented diacylations under Friedel-Crafts conditions.7
2,3-Disubstituted butadienes are also accessible by Grignard addition8 or by thermal rearrangement,9 while alkylborane addition10 is a means of obtaining 2-alkylbutadienes (eq 3).
With Sodium Amide, the bisacetylide anion is formed, which on being quenched with Iodomethane gives 1,3-pentadiyne.11 Alternatively, the carbanion can be treated with a carbonyl compound to obtain dialkynyl alcohols. In one instance a dialkynyl alcohol has been elaborated to a hydroxy fatty acid (eq 4)12 and in the other, following a different strategy, to a marine natural product.13
Polycyclic compounds are accessible by successive addition of two carbenes under rhodium catalysis (eq 5).
These can be obtained by addition of dithiocarbonate followed by desulfurization, as an alternative to the traditional Zn reduction (eq 6).
A novel allenol nucleoside16 with pronounced anti-HIV activity is synthesized making use of the base-catalyzed alkyne-allene rearrangement. The allene nucleoside can be cyclized to the dideoxydidehydronucleoside under more basic conditions (eq 7).
These are useful as potential alkylating agents in cancer chemotherapy and can be obtained by a 1,3-dipolar addition of the reagent to a glycosyl azide.
The reagent is used as a coupling promoter to obtain biaryls from aryl Grignard reagents.18 1,4-Bisthioglycosyl-2-butene trimerizes under transition-metal catalysis to give cluster glycosides.19
A. V. Rama Rao
Indian Institute of Chemical Technology, Hyderabad, India