DIMERIZATION OF CYCLOPROPANECARBONITRILE MEDIATED BY GRIGNARD-REAGENTS - FORMATION OF HIGHLY SUBSTITUTED PYRIDINES

The reaction of cyclopropanecarbonitrile with ethylmagnesium bromide i n diethyl ether followed by quenching with malononitrile gave the expe cted 2-cyano-3-cyclopropylpent-2-enonitrile (1a) in high yields. When the solvent was changed to tetrahydrofuran (THF) using ethylmagnesium chloride, low yields of 1a (12%) were obtained; the main products were two pentasubstituted pyridines, chloroethyl)-3-cyano-6-cyclopropyl-4- ethylpyridine (2a, 70%) and -(3,3-dicyanopropyl)-6-cyclopropyl-4-ethyl pyridine (2c, 10%). In addition, their isomers, chloroethyl)-3-cyano-4 -cyclopropyl-6-ethylpyridine (3a, 7%) and -(3,3-dicyanopropyl)-4-cyclo propyl-6-ethylpyridine (3c, 1%), were observed and identified by combi ned gas chromatography-mass spectrometry (GC-MS). When methylmagnesium chloride was used (solvent THF), in addition to 1b and the isomers 2d , 2e, 3d and 3e, a tetrasubstituted pyridine, 2-amino-3-cyano-4,6-dicy clopropylpyridine (11), was formed. Similar reaction between cycloprop yl-magnesium bromide and cyclopropanecarbonitrile gave after hydrolysi s about equal yields of dicyclopropyl ketone and a diketone, 1,1-di(cy clopropanecarbonyl)cyclopropane (8b). The structures of 2c and 2d were established by X-ray crystallography.