Hexamethyl-2,3-dihydropyrazine

Although hexamethyl-2,3-dihydropyrazine 1,4-dioxide (166) does not exhibit typical nitrone properties, oxaziridines are nevertheless formed on photolysis with light of wavelength greater than 300 nm, only the monooxaziridine (167) is formed, whereas with light of wavelength down to 200 nm, cis- (168) and trans- (169) dioxaziridines are obtained.148... 

The preparation of some 2,3-dihydropyrazines from a, -dicarbonyl compounds with a,0-diamino compounds has been recorded in Section 11.2 (330, 330a, 331, 333, 334, 338-344, 349, 356, 357), with further data given in references 6, 337, 345, and 1547-1549. In addition hexamethyl-2,3-dihydropyrazine (16) has been prepared from 2,3-diamino-2,3-dimethylbutane and butane-2,3-dione (1550). Condensation of oxalyl chloride with diiminosuccinonitrile (10) in ether has been shown to give 2,3-dichloro-2,3-dicyano-5,6-dihydroxy-2,3-dihydropyrazine (17) (383). 

It has been claimed (25) that 2,3-diphenyl-5,6-dihydropyrazine when heated with acetic or benzoic anhydride gives a derivative of the 1,4-dihydropyrazine ring system, but this has been shown by Chen and Fowler (1562) to be in error [the products have been shown to be 1,4-diacetyl(or dibenzoyl)-5,6-diphenyl-l,2,3,4-tetrahydropyrazine (26, R = Me or Ph), respectively, together with 23-diphenyl-pyrazine]. Hexamethyl-2,3-dihydropyrazine cannot undergo oxidation to a pyrazine, but it rapidly dimerized in air in the presence of hydrochloric acid to give compound (27, X = Cl) (also prepared as the iodide with iodine in ether) (1550). 

Reduction of 2,2,3,3,5,6-hexamethyl-2,3-dihydropyrazine 1,4-dioxide (78) with sodium borohydride gave l,4-dihydroxy-2,2,3,3,5,6-hexamethylpiperazine (555) and attempted deoxygenation of (78) by zinc and hydrochloric acid gave the bishydroxylamine (79) (555). Compound (78) did not form benzylidene derivatives with benzaldehyde (555) and it was only slowly attacked by selenium dioxide one equivalent of selenium dioxide required 5 days boiling under reflux before the nitrone was completely reacted, and the product was thought to be 6-formyl-... 

The photochemical isomerization of hexamethyl-2,3-dihydropyrazine 1,4-dioxide has been investigated (1606). 

The method first described by Conant (1580) for preparing hexamethyl-2,5-dihydropyrazine from 3-methylbutanone with warm aqueous alkaline potassium ferricyanide has been expanded into a simple one-step selective way of preparing a-amino-a,Q -dialkyl ketones and/or their self-condensation products, hexaalkyl-... 

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