Photochemistry of acyloxymethyl(benzyl)silanes. Evidence for the primary formation of a benzyl-silyl radical pair and mechanism of free-radical 1,2-(carbon .fwdarw. silicon)-acyloxy migration

Abstract

BLM concentrations was suggested by the reversal of this trend upon aeration of the reaction mixtures.The demonstration that a synthetic dodecanucleotide can act as a sequence-selective substrate for BLM provides a powerful new tool for the study of this antitumor antibiotic at its putative therapeutic locus and a novel approach for the study of naturally occurring and synthetic DNA interactive agents. Acknowledgment.We report herein novel photochemistry of [(acyloxy)methyl]-benzyldimethylsilanes as well as benzyltrimethylsilane.* The results provide not only definitive evidence for the formation of a benzyl radical-silyl radical pair in the primary photochemical process but also an important insight into the detailed mechanism for free-radical 1,2 (C -Si) acyloxy migration found r e~e n t l y .~

Nanosecond Laser Flash Photolysis and Steady-State Photolysis Studies of Benzyltrimethylsilane and Trimethylsilyldiphenylmethane

“…There have been, however, few reports on the study of direct photolysis of benzylsilanes. ,,, Valkovich et al studied the direct photolysis of 1,1-dimethyl-2-phenyl-1-silacyclobutane in degassed methan-[ 2 H]-ol at 0 °C and obtained 3-phenyl-[3- 2 H 1 ]-propyldimethylmethoxysilane in quantitative yield. They proposed that cleavage of the Si−C (benzyl) bond took place to form a zwitterion in which the benzyl carbon is negatively charged and the silyl group is positively charged.…”

The one- and two-photon photochemistry of benzylsilacyclobutanes, acyclic benzylsilanes, and 1,1,2-triphenylsilacyclobutane

“…While the photoisomerization of 1 and 2 to the corresponding isotoluene derivatives has precedent in the photochemistry of other benzyl compounds (24), it has not been reported previously for benzylsilanes. Benzyltrimethylsilane (3) was first reported to be inert to photolysis in solution (20), but Kira et al (19) later found that extended photolysis of the compound in hydrocarbon solution leads to the inefficient formation of ortho-tolyltrimethylsilane (18a), which they suggested to arise from a minor reaction of benzyl and trimethylsilyl radicals produced by homolysis of the benzyl carbon-silicon bond in the benzylsilane. More recently, spectroscopic evidence for the formation of free benzyl radicals upon photolysis of 3 in an ethanol matrix at 77 K has been reported by Hiratsuka et al (29).…”

“…Hexanes and methanol (BDH Omnisolv), cyclohexane-d 12 (Cambridge Isotope Laboratories), benzyl bromide (Aldrich), benzyltrimethylsilane (3, Aldrich), dimethylphenylsilane (19,Aldrich), and chlorodimethylphenylsilane (Aldrich) were used as received from the suppliers. Tetrahydrofuran (BDH) was distilled from sodium.…”

“…These two compounds exemplify two different photophysical situations -one in which the benzyl group is the primary chromophore in the molecule (1) and one in which the role of primary chromophore is shared between it and the silacyclobutane ring via a second phenyl group at-tached to silicon (2). Previous work suggests that benzylsilanes generally exhibit very low photoreactivity upon direct excitation in condensed phases (19). We thus wondered whether benzylsilacyclobutanes might show similar reactivity toward silene photoextrusion as is possessed by other simple silacyclobutane derivatives, with minimal complications from competing reactions due to the benzylic substituent.…”

Synthesis and photochemical properties of 2,2′-silaspirobiindan and related compounds

“…[1][2][3] Kira and Sakurai have previously reported the photorearrangement of benzyltrimethylsilane (1a) and (acyloxy)methyl-substituted benzylsilanes via C-Si photo-cleavage. 4 Very recently, Hiratsuka et al have clarified the photophysical and photochemical processes of 1a at 77 K and the molecular structure of its excited state by MNDO-PM3 calculations. 5 However, little is known about the synthesis and photochemical behaviour of 2,2'-silaspirobiindan and its related group 14 element compounds, 6 although spiro conjugated compounds having two perpendicular π-electron systems have been widely investigated.…”