Steric Enhancement of the Chemiluminescence of Luminols.

A surprising 20-fold increase in chemiluminescence efficiency was observed for dialkyl luminol derivatives in comparison with the parent compound. This effect could be a direct consequence of steric gearing which facilitates the transition from the intermediate endoperoxide to the electronically excited phthalate. Mechanistic aspects of this process have been supported by computational calculations (CASPT2//CASSCF).

Modular synthesis of cyclic cis- and trans-1,2-diamine derivatives.

Structurally diverse carbocycles with two vicinal nitrogen-substituents were prepared in expedient three-component reactions from simple amines, aldehydes, and nitroalkenes. trans,trans-6-Nitrocyclohex-2-enyl amines were obtained in a one-pot domino reaction involving condensation, tautomerisation, conjugate addition, and nitro-Mannich cyclisation. Upon employment of less nucleophilic carboxamides, a concerted Diels-Alder cycloaddition mechanism operated to give the corresponding cis,trans-nitrocyclohexenyl amides. Both types of substituted carbocycles offer ample opportunities for chemical manipulations at the core and periphery. Ring oxidation with MnO2 affords substituted nitroarenes. Reduction with Zn/HCl provides access to various trans- and cis-diaminocyclohexenes, respectively, in a straight-forward manner. With enantiopure secondary amines, a two-step synthesis of chiral nitrocyclohexadienes was developed (82-94% ee).

Practical three-component synthesis of crowded arenes with donor-acceptor substitution.

An operationally simple two-step synthesis of substituted anilides has been developed. The methodology utilizes carboxamides, aldehydes, and olefins (or alkynes) as cheap starting materials and relies upon the sequential combination of condensation, cycloaddition, and oxidation reactions. The intermediate cycloadducts display various functional groups (e.g. Br, OAc, NR(2), COR, Cbz) for further chemical manipulation at the ring periphery or core. Upon oxidation with MnO(2), highly crowded anilides with up to four further substituents (alkyl, aryl, carboxylate, cyano, nitro, bromo) can be prepared in good overall yields.

On the photophysical properties of new luminol derivatives and their synthetic phthalimide precursors.

The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy. UV spectra in gas phase and DMSO solution were calculated by TD-DFT which revealed the existence of two low-energy excited singlet states with strong pH-sensitivity.