Kinetics and Mechanism of Photocycloaddition of Deoxyuridines to 2,3‐dimethyl‐2‐butene

Abstract

The mechanism of photocycloaddition of 2'-deoxyuridine (1a) and thymidine (1b) to 2,3-dimethyl-2-butene (Bu) in acetonitrile by UV irradiation has been studied. The reciprocal quantum yield for the cycloaddition increased linearly with reciprocal concentrations of Bu in acetonitrile to give limiting quantum yields at infinite concentration of Bu as 0.030 and 0.0096 for 1a and 1b, respectively. This shows that the cycloaddition proceeds in a two-step mechanism between the triplet state of 1 and Bu through biradical intermediates. Addition of cis-1,3-pentadiene quenched the reaction obeying the Stern-Volmer equation. The above quenching experiments and laser transient spectroscopy revealed that the triplet state of 1a reacts with Bu with much larger rate constant (1.3-1.6 x 10(9) M-1 s-1) than that of 1b (4-5 x 10(7) M-1 s-1) reflecting larger steric hindrance exerted in the reaction of 1b than that of 1a.

Photoinduced Electron Transfer between Acenaphthylene and Tetracyanoethylene: Effect of Irradiation Mode on Reactivity of the Charge-Transfer Complex and the Resulted Radical Ion Pair in Solution and Crystalline State

“…Apparatus for Photolysis. Apparatus kit for preparative-scale irradiation in solution has been described elsewhere. ,, As the light source, a high-pressure mercury lamp was employed with color-glass filters. For isolation of light of wavelength longer than 300 nm, a jacket made of Pyrex glass was employed in stead of a quartz one.…”

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…The rate constants for the intermolecular reactions were determined as 1.3–1.6 × 10 9 M –1 s –1 and 4–5 × 10 7 M –1 s –1 . 771 …”

“…The rate constants for the intermolecular reactions were determined as 1.3−1.6 × 10 9 M −1 s −1 and 4−5 × 10 7 M −1 s −1 . 771 The diastereoselectivity of intramolecular reactions in which the olefin component was tethered to a hydroxy group of the nucleoside was found to be high. 772 The intramolecular [2 + 2] photocycloaddition of thymine glycoconjugates was used by Lindhorst and co-workers to prepare multivalent carbohydrates.…”

“…= 71/29) when performed under sensitized conditions. The rate constants for the intermolecular reactions were determined as 1.3–1.6 × 10 9 M –1 s –1 and 4–5 × 10 7 M –1 s –1 …”

Photoinduced electron transfer between acenaphthylene and 1,4-benzoquinones. Formation of dimers of acenaphthylene and 1 ∶ 1-adducts and effect of excitation mode on reactivity of the charge-transfer complexes

“…The merry-go-round apparatus for irradiation is described elsewhere. 39 Filtering of > 420 nm and > 500 nm light was according to the previous method. 40…”