Synthesis of Spiroindolinonaphthoxazines and Analogues

The commercially available spirooxazines are based on the spiroindolinonaphthoxazines (1.11) ring structure. The synthetic route to this ring system involves the reaction of a l-hydroxy-2-nitoso bearing aromatic ring with a 2-aUcylidene heterocycle, such as Fischer s base (1.6 R = H). The naphthoxazines are the derivatives of choice 

The spiroindolinonaphthoxazine derivatives became commercially important compounds once detailed research work led to products which overcame many of their initial weaknesses, such as relatively poor fatigue resistance and a poor colour range (550-620 nm). The important positions for substitution in the ring of (1.11) are the 5-position which has a large effect on the colour, the 6 -position, which has a major effect on both the colour and properties such as optical density (OD) and molar absorption coefficient and the alkyl group on position 1, which has a kinetic effect on the rate of loss of colour back to the colourless state.  

The important products bearing amino substituents in the 6 -position are synthesised from 4-substituted-l-nitroso-2-naphthols (1.14), which are prepared from (1.12) via (1.13).  

Another group of commercially important spirooxazines are those where the naphthalene ring is replaced by quiinoline to give the spiroindolinopyridobenzoxazines (1.17). These are synthesised by reaction of 5-nitroso-6-hydroxyquinoline (1.16) with alkyl substituted 2-methyleneindolines (1.15).  

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