Azo Bridges from Azines, XXII. [2 + 2] Photocycloaddition and 1,5‐Laticyclic Conjugation Between Parallel Azo Groups and π‐Systems The Symmetry Criterion in Azo‐Carbonyl Interactions

Abstract

AbstractThe known 1,5‐lacticyclic interaction between parallel CC/ NN bridges in 1 in expressed by a bathochromic shift of the azo n‐π* transition of +7–10 nm. A CCCN bridge (2, 6) increases the bathochromic shift slightly, whereas a CC–OSiR3 bridge (3) cases a hypsochromic shift of −6 nm. In a R3SiO–C = C–CN bridge (4) the effect of the two substituents cancel each other. All these compounds (1–6, 13) undergo quantitative [2 + 2] photocycloaddition by n‐π* excitation. A novel transannular interaction between azo and carbonyl (20, 21: +8 nm) and 1,2‐dicarbonyl groups (24: ca. +20 nm) is observed. From photoelectron spectra and MO calculations neighboring group effects on the orbital energies in 20, 21, and 24 are assessed and discussed.