Steric effect on photochemistry of benzyl ester derivatives

Goshima, Toshiyuki; Itoh, Yoshifumi; Kojima, Masanobu; Karatsu, Takashi

doi:10.1016/s1010-6030(99)00136-7

Cited by 6 publications

(8 citation statements)

References 31 publications

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“…When low molecular weight model compounds, BP, MBP, and BA, were photolyzed, seven benzylic products were identified by GC and GC mass spectroscopy (MS): The formation of products 1–7 is rationalized by homolytic cleavage of the benzyl–heteroatom bond,18, 19, 26, 27 that is, the products are all derived from benzyl radicals: 1 and 3 are formed by coupling with alkyl and benzyl radicals, respectively; 2, by hydrogen‐atom abstraction; and 4–6, by reaction with solvents. A trace amount of 7 may be an oxidized product 19. For all polymers, the products except a polymeric one corresponding to 1, which could not be detected by GC, were obtained, indicating that the degradation of ester groups in the polymers proceeds by the same mechanism.…”

Section: Resultsmentioning

confidence: 99%

“…1‐Phenylethyl methacrylate (MBMA) and benzyl acrylate (BA) were synthesized by the reaction of the corresponding alcohols with methacryloyl or acryloyl chloride in triethylamine–tetrahydrofuran (THF) mixtures16 and purified by distillation under reduced pressure. Monomeric model compounds are those reported previously 19…”

Section: Methodsmentioning

confidence: 99%

“…Most of the photoproducts were commercially available. 2,2‐Dimethyl‐3‐phenylbutane and meso ‐ and dl ‐2,3‐diphenylbutane were isolated from the products of preparative photolysis of 1‐phenylethyl pivalate (MBP) 19…”

Section: Methodsmentioning

confidence: 99%

“…A 0.01 M solution (4 mL) of the ester in CH 2 Cl 2 was placed in a quartz tube, purged with argon or oxygen gas for 10 min, and then irradiated for 1 h at 25°C. The samples were analyzed by GC as described previously 19…”

Section: Methodsmentioning

confidence: 99%

“…We speculated some contribution of steric hindrance of substituent groups and polymer chains to the photocleavage. In fact, a detailed study on the photochemistry of α‐substituted naphthylmethyl and benzyl alkanoates indicated the importance of steric hindrance around the ester bond 18, 19…”

Section: Introductionmentioning

confidence: 99%

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Photolysis of poly(benzyl methacrylate)s and poly(benzyl acrylate)s in solution and films

Itoh

Goshima

Shirai

2001

J of Applied Polymer Sci

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Methacrylate and acrylate copolymers containing benzyl or 1-phenylethyl groups and their monomeric model compounds were irradiated with a 254-nm light in CH 2 Cl 2 and solid films. Low molecular weight and polymeric products were analyzed by gas chromatography (GC) and NMR spectroscopy, respectively, and main-chain scission efficiencies were determined by gel permeation chromatography (GPC). The results indicate that the ester bond cleavage in the side chain produces alkyl radicals in the main chain, leading to main-chain scission and crosslinking. The higher stability of tertiary alkyl radicals formed in methacrylate polymers lead to the predominant main-chain scission in solution. On the other hand, acrylate polymers were less susceptible to photodegradation. The degradabilities of the polymer films reflected those of the polymer solutions, although crosslinking preferentially occurred. The distinct effect of oxygen on the degradation was also observed in solution and films.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photolysis of poly(benzyl methacrylate)s and poly(benzyl acrylate)s in solution and films

Itoh

Goshima

Shirai

2001

J of Applied Polymer Sci

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A Time‐Resolved Spectroscopic Study of the Bichromophoric Phototrigger 3′,5′‐Dimethoxybenzoin Diethyl Phosphate: Interaction Between the Two Chromophores Determines the Reaction Pathway

Kwok

et al. 2010

Chemistry A European J

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3',5'-Dimethoxybenzoin (DMB) is a bichromophoric system that has widespread application as a highly efficient photoremovable protecting group (PRPG) for the release of diverse functional groups. The photodeprotection of DMB phototriggers is remarkably clean, and is accompanied by the formation of a biologically benign cyclization product, 3',5'-dimethoxybenzofuran (DMBF). The underlying mechanism of the DMB deprotection and cyclization has, however, until now remained unclear. Femtosecond transient absorption (fs-TA) spectroscopy and nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopy were employed to detect the transient species directly, and examine the dynamic transformations involved in the primary photoreactions for DMB diethyl phosphate (DMBDP) in acetonitrile (CH(3)CN). To assess the electronic character and the role played by the individual sub-chromophore, that is, the benzoyl, and the di-meta-methoxybenzylic moieties, for the DMBDP deprotection, comparative fs-TA measurements were also carried out for the reference compounds diethyl phosphate acetophenone (DPAP), and 3',5'-dimethoxybenzylic diethyl phosphate (DMBnDP) in the same solvent. Comparison of the fs-TA spectra reveals that the photoexcited DMBDP exhibits distinctly different spectral character and dynamic evolution from those of the reference compounds. This fact, combined with the related steady-state spectral and density functional theoretical results, strongly suggests the presence in DMBDP of a significant interaction between the two sub-chromophores, and that this interaction plays a governing role in determining the nature of the photoexcitation and the reaction channel of the subsequent photophysical and photochemical transformations. The ns-TR(3) results and their correlation with the fs-TA spectra and dynamics provide evidence for a novel concerted deprotection-cyclization mechanism for DMBDP in CH(3)CN. By monitoring the direct generation of the transient DMBF product, the cyclization time constant was determined unequivocally to be approximately 1 ns. This indicates that there is little relevance for the long-lived intermediates (>10 ns) in giving the DMBF product, and excludes the stepwise mechanism proposed in the literature as the major pathway for the DMB cyclization reaction. This work provides important new insights into the origin of the 3',5'-dimethoxy substitution effect for the DMB photodeprotection. It also helps to clarify the many different views presented in previous mechanistic studies of the DMB PRPGs. In addition to this, our fs-TA results on the reference compound DMBnDP in CH(3)CN provide the first direct observation (to the best of our knowledge) showing the predominance of a prompt (approximately 2 ps) heterolytic bond cleavage after photoexcitation of meta-methoxybenzylic compounds. This provides insight into the long-term controversies about the photoinitiated dissociation mode of related substituted benzylic compounds.

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Selectivity in photolysis of benzyl acetate and benzyl hexanoate upon cyclodextrin complexation

Annalakshmi

Pitchumani

2006

Journal of Photochemistry and Photobiology A: Chemistry

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Steric effect on photochemistry of benzyl ester derivatives

Cited by 6 publications

References 31 publications

Photolysis of poly(benzyl methacrylate)s and poly(benzyl acrylate)s in solution and films

Photolysis of poly(benzyl methacrylate)s and poly(benzyl acrylate)s in solution and films

A Time‐Resolved Spectroscopic Study of the Bichromophoric Phototrigger 3′,5′‐Dimethoxybenzoin Diethyl Phosphate: Interaction Between the Two Chromophores Determines the Reaction Pathway

Selectivity in photolysis of benzyl acetate and benzyl hexanoate upon cyclodextrin complexation

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