Stereospecificity of Diels–Alder Reactions Validated Using Ab Initio Calculations: Synthesis of Novel Coumarin and Phenanthridine Derivatives

Abstract

A new series of coumarin derivatives (2–5) was synthesized by reaction of phenylsulfonylacetonitrile (1) with 2-hydroxy-1-naphthaldehyde and/or salicyaldehyde. Compounds 3 and 5 were converted to the corresponding phenanthridine analogs 6 and 7, respectively. Compound 9a was treated with different dienophiles to furnish the endo adducts of compounds (11a–d) rather than the exo adducts. Ab initio calculations at the Hartree-Fock (HF) level using the basis set 6-31 G (d,p) was used to study and validate the stereospecificity of compounds 11a–d and showed clearly that the endo adducts were thermodynamically favorable. PM3 parameters also showed that the endo adducts are thermodynamically and kinetically favorable. Tetrahydrobenzochromenone (11) was synthesized and allowed to react with different aromatic diazonium salts to give the corresponding 4-arylazo derivatives (13), which were converted to the corresponding diazaindenophenanthrene derivatives (14) by reaction with o-diamines.