Azines with Grignard reagents

The synthesis of 1,2,4-triazines 3 by reaction of 1,2,4-triazin-3(2//)-ones 1334 or 1,2,4-tri-azin-5(2//)-ones 2335 with Grignard reagents in an addition/elimination sequence has also been reported. 

The transition metal catalyzed carbon-carbon bond formation between organomagnesium reagents and aryl (vinyl) halides has been one of the pioneering entries into cross-coupling chemistry. The reaction has been widely utilized since than in azine chemistry,22 with the limitation that the functional group tolerance of Grignard reagents is only moderate. Here only some of the more recent developments will be mentioned. 

Unsymmetrically -substituted borazines can be prepared by the reaction of IV-substituted borazines or h-trihalogeno-N-substituted borazines and the appropriate amount of Grignard reagent (94). Borazines unsymmetrically substituted on nitrogen have been prepared by the reaction of Hthium borohydride and ammonium chloride and alkyl ammonium chlorides (105,106), and by Uthiation of B- trime thylb o r azine followed by reaction with alkyl halides (107). 

Nucleophilic substitution in electrophilic azine positions with nonstabi-lized carbanionic reagents is difficult. It has been found, however, that sulfoxides derived from an electrophilic azine position can react with a Grignard reagent with replacement of the sulfinyl group and carbosubstitu-tion [90AHC(48)1]. 

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