Flash Photolysis of 1,3-Dichloro-1,3-diphenylpropane in Polar Solvents:  Generation of a Stabilized γ-Chloropropyl Cation, Subsequent Formation of a Propenyl Cation, and Nucleophilic Trapping of Both Cations

Abstract

Photolysis of 1,3-dichloro-1,3-diphenylpropane (1) in 2,2,2-trifluoroethanol at 266 nm leads to a γ-chloropropyl cation (2a) following loss of chloride ion. Kinetic evidence has been obtained for the interconversion between the open chain cation and the corresponding cyclic chloronium ion (2b); thermal loss of hydrogen chloride gives the 1,3-diphenyl-2-propenyl cation (3). The formation of this species occurs through a monophotonic process; the involvement of a two-photon process in the photoheterolysis of dihalide 1 has been ruled out by studying the formation of cation 3 from 1 at different laser intensities. The lack of power dependence implies that 3-chloro-1,3-diphenylpropene (4) is not an intermediate in the photoheterolysis of dihalide 1. The reaction of both cationic intermediates (2 and 3) with different nucleophiles has also been examined. Finally, two-laser two-photon experiments have allowed the study of the photoisomerization of E,E-3 into Z,E-3.

Chromoselective access to Z- or E- allylated amines and heterocycles by a photocatalytic allylation reaction

“…4a, red line). Two new absorption bands at 360 and 490 nm are clearly observed, which correspond to intermediates I and II , respectively, based on literature data 45 . The lifetime of the carbocation INT II also depends on the nucleophilicity of the anionic leaving group (see Supplementary Information Fig.…”

One- vs Two-Photon Processes in the Photochemistry of 1,n-Dihaloalkanes

“…Photolysis of 1,3-dichloro-1,3-diphenylpropane in 2,2,2-trifluoroethanol (TFE) at 266 nm leads to the γ-chloroalkyl cation. Similarly to other γ-chloroalkyl cations, this species thermally loses hydrogen chloride, leading to the ( E,E )-1,3-diphenylpropenyl cation with characteristic absorption at λ max 490 nm (Figure ) . The possibility of two-photon generation of the latter from the dichloride has been ruled out by studying its formation at different laser intensities.…”

“…Finally, the ( E,E )-1,3-diphenylpropenyl cation photoisomerizes to its ( Z,E ) stereoisomer either in rigid media or in solution . In TFE, ( Z,E )-1,3-diphenylpropenyl cation undergoes thermal reversion with a lifetime of 3.5 μs at room temperature.…”

Three-Color Three-Laser Photochemistry of Di(p-methoxyphenyl)methyl Chloride

“…As the simplest multilaser chemistry, two-laser chemistry of short-lived species such as excited molecules and reactive intermediates in liquid phase has been extensively investigated by various groups. For example, Miranda et al have reported that heterolytic cleavage of C−Cl bond proceeds to give α-chloroalkylbenzyl cation and chloride ion during the first 266-nm laser flash photolysis of dichlorodiphenylalkanes, , followed by dehydrochlorination of the cation to give α- E -allylbenzyl cation, and that the α- E -allylbenzyl cation isomerizes to the Z -isomer with the second laser excitation at 480 or 532 nm. Ouchi et al have reported that two-step homolytic cleavages of two C−Br or C−Cl bonds proceed to give a biradical during two-color two-laser photolyses of 1,8-bis(bromomethyl)- and 1,8-bis(chloromethyl)naphthalenes using the first 193-, 248-, or 308-nm and second 351-nm excimer lasers .…”