23511-42-4

2,3-Dialkylquinoxalines (4), which are available from the reaction of benzofuroxan (1) with ketones and subsequent reduction of the 2,3-dialkylquinoxaline N,N'-dioxides (3), are converted to 2,3-dialkylpyrazines (6) by oxidation-decarboxylation steps.

A cosmetic composition for imparting to human skin after exposure to sunlight a coloration resembling a natural tan comprises a cosmetic vehicle suitable for topical application to the skin and an effective amount of at least one compound of the formula STR1 wherein R1 and R2 each independently represent hydrogen, an aliphatic radical having 1-18 carbon atoms, carbalkoxy having 2-5 carbon atoms, acyl having 2-5 carbon atoms, aryl, aryl substituted by alkyl having 1-4 carbon atoms or hydroxy, a heterocycle containing 4-6 members, substituted or not by alkyl having 1-4 carbon atoms, halogen or hydroxy, or R1 and R2 together form a saturated ring containing 4-12 chains, optionally substituted by alkyl having 1-4 carbon atoms, halogen or hydroxy, or bridged and containing a heteroatom selected from N, O or S; and R3 represents hydrogen, a lower aliphatic group containing 1-6 carbon atoms, lower alkoxy containing 1-4 carbon atoms or halogen, with the proviso that R1, R2 and R3 are not hydrogen simultaneously; and an acid addition salt thereof.