Effect of Alkyl Substituents on Photorelease from Butyrophenone Derivatives

Abstract

Photolysis of 1a yields 4a in argon-saturated methanol, whereas 1b is photostable. Laser flash photolysis of 1a in acetonitrile shows formation of biradical 2a (lambda(max) = 340 nm, tau = approximately 60 ns), which undergoes intersystem crossing to form Z-3a (lambda(max) = 380 nm, tau = 270 ns) and E-3a (lambda(max) = 380 nm, tau = 300 ms). Z-3a regenerates the starting material, whereas E-3b undergoes intramolecular lactonization to release the alcohol moiety and form 4a. Similar laser flash photolysis of 1b shows formation of biradical 2b (lambda(max) = 340 nm, tau = 1.9 micros in acetonitrile), which is longer-lived than 2a is. However, 2b only undergoes intersystem crossing to form Z-3b (lambda(max) = 380 nm, tau = 4.3 micros). Calculations demonstrate that intramolecular pseudo hydrogen bonding between the OH moiety and the radical centered on the isopropyl carbon in 2b and the bulkiness of the isopropyl group prevent the necessary rotation to form E-3b. In comparison, 2a does not form an intramolecular pseudo hydrogen bond between the methylene radical center and the OH group, and as a consequence, it undergoes intersystem crossing to form both E- and Z-3a.

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

“…80a In addition, the 4-oxo-4- o -tolylbutanoate 23 releases methanol by a photoenolization-induced lactonization process (Scheme 14). 81 …”

Phenylethanol derivatives as triplet sensitizers for 1‐azidoadamantane

“…Thus, unrestricted Becke, three‐parameter, Lee–Yang–Parr (UB3LYP) optimization of 1, 2, 3 and 4 yielded energies that are in good agreement with those obtained from TD‐DFT calculations. We have previously shown that UB3LYP significantly underestimates the adiabatic energy of triplet ketones with ( n ,π*) configuration, whereas UB3LYP assessment of the adiabatic energy of triplet ketones with (π,π*) configuration is excellent …”

Photoenolization of o‐Methylvalerophenone Ester Derivative

“…Esters 1 , 9 and 10 all form long‐lived E‐photoenols, but each reacts differently, and therefore yields insight into the factors that govern their reactivity. Photoenol E‐ 11 releases its methanol moiety and forms lactone 13 , whereas E‐ 12 does not release its alcohol moiety spontaneously and only undergoes electrocyclic ring closure to form cyclobutanol 14 . The additional ortho ‐methyl substituents on photoenol E‐ 12 make it non‐planar, and this alignment is better for electrocyclic ring closure than that of more planar photoenols .…”

“…In addition, alcohols can also be released through photoenolization of ester derivatives, as long as the photoenolization is followed by spontaneous intramolecular lactonization between the ester and the enol alcohol (Scheme 3) ( [14][15][16][17][18].…”