Synthesis, x-ray structural analysis and photochemistry of novel syn-periplanar bis-azo-skeletons

Proximate, “Parallel‐In‐Plane” Preoriented Bis(diazenes) − In‐Plane Delocalized Bis(homoconjugated) 4N/5(6)e Anions

“…[36] Treatment of tetraacetylcyclohexene 14 [37] with hydrazine had been part of a project [9] to construct allylically peralkylated syn-periplanar bis(diazenes) (kinetically stabilized tetrazetidines) via bis-(isopyrazoles) such as 12 or bis(dihydropyrazines) such as 13.…”

“…[39] With d av ϭ 2.97 Å and ω ϭ 154.3°, the proximity parameters are significantly better than those given in Figure 1 for the parent tetramethyl-B structure. [36] The C s symmetry manifested (CH 3 CN) ϭ 394 nm, ε ϭ 245] was remarkably redshifted, raising speculations that the n-electron pairs of the two ''bridge'' heteroatoms might extend the NϭN/NϭN chromophore through homoconjugation. Irradiation with monochromatic light (254 nm) only produced polymers, but use of a sensitizer (acetone) and n Ǟ π*-excitation selectively gave the ''reluctant'' monodiazene 22 (Scheme 3).…”

Tetraacylethenes as Dienophiles and Hetero Dienes in Two-Step Diels–Alder Reactions

“…[3] [38] Other common di-without any change. In contrast, the spirocyclic dihydropy-certed, however, because a concerted mechanism would have to involve the highly strained, tricyclic boat transition state 28.…”

Highly efficient photometathesis in a proximate, synperiplanar diazene-diazene oxide substrate: retention of optical purity, mechanistic implications

“…tetrazetidine photocycloaddition [reaction (1)]. 2,3 We have recently reported that in the specifically designed very proximate and nearly synperiplanar bisdiazene 1 with its very favourable stereoelectronic prerequisites (d = 2.822 Å, w = 174.2°, X-ray), N 2 elimination still precludes the [p2 + p2] photocycloaddition, but that some photometathesis of its oxide 2 (? 3) does occur (2%) [reaction (2)], most probably through the tetrazetidine oxide.…”

“…3) does occur (2%) [reaction (2)], most probably through the tetrazetidine oxide. 4 Given the quantum yields F -N 2 of 1.00 and 0.02, respectively, for the N 2 elimination from the parent 2,3-diazabicyclohept-2-ene (DBH) and 2,3-diazabicyclooct-2-ene (DBO), 5 the cycloaddition (metathesis) of the isomeric oxide 4 with its oxidized DBH-and 'reluctant' DBO-subunits was expected to be more successful [reaction (3)]. The synthesis of 4 as a racemate and as the (+)-enantiomer and the experimental verification of the above hypotheses are the subjects of this communication.…”