Reaction of N¹, N²‐diarylamidines with chloranil and 2,3‐dichloro‐1,4‐naphthoquinone

Abstract

Abstract Nucleophilic attack by N 2 of N 1 N 2 ‐diarylformamides 1a‐c on C‐2 of chloranil (2) and subsequently by N 1 on C‐1 of 2 initiates the formation of benzimidazolinones 8a‐c. In contrast, when 1b‐e is reacted with 2,3‐dichloro‐1,4‐naphthoquinone (9) , both chlorine atoms are successively substituted by the two nitrogen atoms and 2‐(arylamino)‐3‐( N ‐formylarylamino)‐1,4‐naphthoquinones 13b‐e result, which (probably via their cyclic tautomers 12b‐e ) may be cyclodehydrogenated to form N 1 , N 3 ‐diarylnaphtho[2,3‐ d ] imidazoline‐2,4,9‐triones (as 14b,c ). On the other hand, N 1 , N 2 diarylacetamidines 15a‐d attack 2 and 9 at C‐2 with N 2 but subsequently exert nucleophilic character at the acetamidine α‐carbon attacking C‐1 of 2 and 9 , respectively, thus forming 1‐aryl‐2‐(arylimino)‐3a‐hydroxy‐2,3,3a,6‐tetrahydro‐1 N ‐indol‐6‐ones 18a‐d and 3‐aryl‐2‐(arylimino)‐9b‐hydroxy‐2,3,5,9b‐tetrahydro‐1‐ H ‐benz[ e ]indol‐5‐ones 19b,c , respectively. The latter may be thermally dehydrated to the fully conjugated 2,5‐dihydro‐3 H ‐benz[ e ]indol‐5‐ones 20b,c. Unambiguous structural assignments for 18b and 20c are made on the basis of X‐ray crystal structure analyses.