Ninhydrin as a building block in scaffold-linked chromophoric dyad construction

Abstract

The reaction of ninhydrin with ester-activated cyclobutene epoxide (CE-1) containing the fused 1,4- dimethoxynaphthalene ( DMN ) chromophore, gave adducts formed by 1,3-dipolar cycloaddition at the central (C 2)-CO (major) and the outer (C 1,3 )-CO (minor) positions. Conversion of the minor adduct to quinoxalines ( QIN ) by reaction with o-phenylenediamines at the α-dione moiety, albeit in poor yield, led to spiro-DMN-1,4 σ σ σ σ-QIN dyad in which the plane of the chromophore was orthogonally orientated yet angled to the plane of the DMN chromophore. Reaction of ninhydrin with o-phenylenediamines yielded the corresponding 11-oxoindeno(1,2-b)quinoxalines which were coupled with CE-BLOCKs to form spiro adducts by reaction at the carbonyl site; the product from CE -1 was identical with that formed above. Another class of spiro-fused dyads was produced by reaction of ninhydrin with a primary amine followed by cycloaddition of CE-BLOCKs at the carbonyl site, where the amine was available to deliver one chromophore and the CE-BLOCK another.