[1070-71-9] · C3HN · Propynenitrile · (MW 51.05)
Alternate Names: cyanoacetylene; propiolonitrile.
Physical Data: mp 5 °C; bp 41 °C.
Solubility: sol benzene, EtOH, acetonitrile, cyclohexane, toluene, ether.
Analysis of Reagent Purity: IR (gas) 863, 2077, 2272, 3327 cm-1.
Preparative Method: not commercially available, but can be prepared6,7 on a several gram scale by the dehydration of propynamide (propiolamide) with Phosphorus(V) Oxide (eq 1). The reactants are well ground together under nitrogen, and upon subjection of the resulting solid mixture to high temperature treatment, propynenitrile is collected as a distillate in a receiver held at 5 °C.
Handling, Storage, and Precautions: decomposes in solution; sensitive to air and light.
Propynenitrile is an excellent conjugate addition electrophile. Simple transformations of this sort are given in eqs 2 and 3,1,7 which show the (Z) stereoselectivity that is expected.
An interesting heterocycle-forming process that depends on nucleophilic conjugate addition to propynenitrile as well as to the reagent's nitrile group is illustrated in eq 4.8 This transformation evidently proceeds through the indicated tricyclic intermediate, which is further transformed hydrolytically in situ.
Propynenitrile affords (Z)-enynes that arise formally from the conjugate addition of an acetylide nucleophile. This clever transformation is brought about by the in situ conjugate addition of bromide to give (Z)-3-bromopropenenitrile and its subsequent palladium-induced coupling with an alkyne (eq 5).2
This reagent can be involved in the Ritter reaction, but with only modest success (eq 6); other examples proceed even less efficiently.9 A more successful transformation that operates on the nitrile group is shown in eq 7.9
Propynenitrile engages suitable dienes in Diels-Alder cycloadditions. For example, a neat mixture of propynenitrile and Cyclopentadiene held at rt affords the expected bicyclo[2.2.1]heptadiene product in good yield (eq 8).10 A more elaborate example is shown in eq 9,3 in which the regiochemical directive effects of the substituents converge to give the cyclohexadiene product shown.
Reactions of this type include examples involving nitrones (eq 10)4 and diazo compounds (eq 11).5
Two ring-forming transformations brought about with this reagent that are not mechanistically straightforward are illustrated in eqs 12 and 13. In eq 12, two molecules of propynenitrile are incorporated in the product, whose structure was determined by X-ray crystallography.6 Eq 13 depicts an unusual cyclooctatetraene synthesis.11
Charles S. Swindell
Bryn Mawr College, PA, USA