c 1 c 6 alkyl c 1 c 6 alkoxy groups u2018 s u2019 represents integers from 0 1 2 and 3 r 2 r 3 may be same or different and independently selected from the group comprising of hydrogen optionally substituted c 1 c 6 alkyl c 1 c 6 alkoxy c o r b c o nr c r d groups r b is selected from the group comprising of hydrogen optionally substituted c 1 c 6 alkyl c 1 c 6 alkoxy groups r e and r d are independently selected from the groups comprising hydrogen optionally substituted c 1 c 6 alkyl unsubstituted or substituted aryl groups as used herein the term u201c heterocycle u201d or u201c heterocyclic system u201d is intended to mean a stable 5 to 8 membered monocyclic or bicyclic or a 9 to 16 membered polycyclic heterocyclic ring which may be saturated partially saturated or unsaturated and which consists of carbon atoms and further comprises from 1 to 4 heteroatoms independently selected from the group consisting of n o and s and including any bicyclic group in which any of the above defined heterocyclic rings is fused to a benzene ring the term heterocycle is intended to include both aromatic as well as non aromatic ring system the nitrogen and sulfur heteroatoms may optionally be oxidized the heterocyclic ring may be attached to its pendant group at any heteroatom or carbon atom which results in a stable structure the heterocyclic rings described herein may be substituted on carbon or on a nitrogen atom if the resulting compound is.