Photolysis of an asymmetrically substituted diazene in solution and in the crystalline state

Discovery and structural characterization of a small molecule 14-3-3 protein-protein interaction inhibitor

“…The N ¼ N bond in diazene compounds is generally sensitive to radiation and is known to undergo photolysis to generate reactive organic radicals (26). We note that another plausible source of the covalent adduct is through imine (Schiff base) formation between the ϵ-amino group of a lysine and the aldehyde group (with the loss of water) on the pyridoxal-phosphate portion of the inhibitor.…”

An efficient synthesis of heptaaryldipyrromethenes from tetraarylcyclopentadienones and ammonium acetate and their extension to the corresponding BODIPYs

“…Unless otherwise stated, phenylacetic acids and benzils were purchased from commercial suppliers and used without further purification. 1,3-Bis(4-methoxyphenyl)propan-2-one, 21 1,3-bis-(3-methoxyphenyl)propan-2-one, 21 1,3-bis(4-(trifluoromethyl)phenyl)propan-2-one, 21 1,3-bis(4-fluorophenyl)propan-2-one, 21 1,3-di-p-tolylpropan-2-one, 22 1,3-bis(4-bromophenyl)propan-2-one, 22 1,3-di([1,1′-biphenyl]-4-yl)propan-2-one, 23 and 1,3-bis-(4-(tert-butyl)phenyl)propan-2-one 24 were synthesized according to published procedures. Tetrahydrofuran (THF) and toluene were distilled from sodium-benzophenone.…”

Taming Radical Pairs in Nanocrystalline Ketones: Photochemical Synthesis of Compounds with Vicinal Stereogenic All-Carbon Quaternary Centers

“…Based on a large number of examples of reactions in crystals where radical combination has been observed, one may conclude that the bond-forming reaction is the path that requires the least amount of atomic and molecular motion. To a rough approximation, the distance between the two α-carbons in a ground-state ketone is approximately 2.7 Å, which is significantly smaller than sum of the van der Waals radii between two carbon atoms (3.4 Å) . While the distance between the carbon centered radical and the hydrogen that would participate in the disproportionation event are often similar, two carbon centered radicals held at a 2.7 Å distance from one another are likely already at the steep descent component of the C–C σ bond potential energy curve.…”

“…To a rough approximation, the distance between the two α-carbons in a ground-state ketone is approximately 2.7 Å, which is significantly smaller than sum of the van der Waals radii between two carbon atoms (3.4 Å). 31 While the distance between the carbon centered radical and the hydrogen that would participate in the disproportionation event are often similar, two carbon centered radicals held at a 2.7 Å distance from one another are likely already at the steep descent component of the C−C σ bond potential energy curve. Once the two carbon-centered radicals assume the required singletstate multiplicity, bond formation in the solid state is likely to be a barrierless process.…”

“…In fact, stable molecules that absorb UV or visible light “instantaneously” increase their energy content by 60–90 kcal/mol, which makes the formation of a wide range of reactive intermediates accessible. We have shown that crystals of diazo compounds, diazenes, pyrazolines, and triazolines can be exposed to UV light to generate carbenes, dialkyl radical pairs, 1,3-dialkyl biradicals and 1,3-alkyl-aminyl radical pairs, respectively, which can go on to give clean products in the solid state. In the case of crystalline ketones ( K , Scheme ), excitation to the n,π* excited state followed by intersystem crossing leads to the triplet state 3 K *, which is able to undergo an α-cleavage reaction to form of a triplet acyl-alkyl radical pair ( 3 RP-1 ) with energetics that depend on the radical-stabilizing abilities of the α-substituents (R 1 -R 3 ).…”