5903-23-1Relevant academic research and scientific papers
Synthesis of peri-cyclobutarenes by thermolysis of [methoxy(trimethylsilyl)methyl]arenes
Engler, Thomas A.,Shechter, Harold
, p. 4247 - 4254 (2007/10/03)
[Methoxy(trimethylsilyl)methyl]arenes are readily prepared by reactions of chlorotrimethylsilane with (α-methoxy)arenylmethyllithium reagents as obtained from (methoxymethyl)arenes and t-BuLi. The [methoxy(trimethylsilyl)methyl]arenes eliminate methoxytrimethylsilane at 525-675 °C/0.05-0.10 mm to yield peri-cyclobutarenes as derived from arenylcarbenes. Of importance is the fact that the initial arenylcarbenes generated insert into adjacent peri C-H bonds and/or isomerize to other arenylcarbenes that insert into their peri C-H bonds to give peri- cyclobutarenes. Thus, flash-vacuum pyrolysis of 1- [methoxy(trimethylsilyl)methyl]naphthalene (13) at 575-675 °C/0.05-0.10 mm yields 1H-cyclobuta[de]naphthalene (6, up to 39%) in practical quantities. 2- [Methoxy(trimethylsilyl)methyl]naphthalene (23) also affords 6 as a major thermolysis product. At 510 °C/0.05-0.10 mm 4-methoxy-1- [methoxy(trimethylsilyl)methyl]naphthalene (29) decomposes to 4-methoxy-1H- cyclobuta[de]naphthalene (31, 46%). Under similar conditions, 2-methoxy-1- [methoxy(trimethylsilyl)methyl]naphthalene (33) converts to 1,2- dihydronaphtho[2,1-b]furan (35, 64%) and naphtho[2,1-b]furan (36, 31%), presumably by insertion of 2-methoxy-1-naphthylcarbene (34) into a C-H bond of its o-methoxy group and then dehydrogenation of the resultant dihydrofuran. Further, 1-[methoxy(trimethylsilyl)methyl]-6-methylnaphthalene (39) pyrolyzes (510 °C/0.10-0.20 mm) to 6-methyl-1-naphthylcarbene (40), which isomerizes in part to 7-methyl-1-naphthylcarbene (49); carbenes 40 and 49 then undergo peri C-H insertion to give 3-methyl-1H- cyclobuta[de]naphthalene (41) and 2-methyl-1H-cyclobuta[de]naphthalene (42) in an 8:1 ratio and a combined yield of 44%. The pyrolytic method is particularly valuable for preparing higher peri single carbon atom bridged arenes such as 4H-cyclobuta[jk]phenanthrene (53, 65%) and 3H- cyclobuta[cd]pyrene (59, 86%).
Photochemistry of 1-naphthylmethyl carbonates and carbamates
Parman,Pincock,Wedge
, p. 1254 - 1261 (2007/10/02)
The photochemistry in methanol of 1-naphthylmethyl phenyl carbonate (3) and 1-naphthylmethyl benzyl carbonate (4) has been studied. Products resulting from both the 1-naphthylmethyl cation and the 1-naphthylmethyl radical are obtained for 3, but only from
Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyl radicals
Hilborn, James W.,Pincock, James A.
, p. 992 - 999 (2007/10/02)
The photolysis of esters 6 and 8 in methanol leads to products resulting from both naphthylmethyl cations and radicals.The product distribution is nearly independent of X for the esters 6 except when X equals methoxy.A mechanism involving initial homolytic cleavage of the carbon-oxygen bond in the excited singlet state of the ester is proposed.Competition between electron transfer in the radical pair to form the ion pair and decarboxylation of the arylacyloxy radical allows calculations of the rates of this decarboxylation process.The ρ values versus ? is close to zero.When X equals methoxy, intramolecular electron transfer occurs with the naphthalene ring serving as the acceptor and the methoxyaromatic as the donor.This exciplex fragments to carbon dioxide and 1-(1-naphthyl)-2-arylethane. Key words: acyloxy radical, decarboxylation, photolysis of benzylic esters.
Intramolecular electron transfer in the photochemistry of substituted 1-naphthylmethyl esters of benzoic acids
DeCosta, D. P.,Pincock, J. A.
, p. 1879 - 1885 (2007/10/02)
Direct excitation of the esters 5 in methanol solvent leads to rapid intramolecular exciplex formation (kex = 1010 s-1 for X = CH3O, Y = CN) with electron transfer from the naphthalene to the benzoate ring.This process dominates the usual fluorescence and reaction of the excited singlet state.The rate of this process can be varied over 103 by suitable change in the substituents X and Y.The electron-transfer rates can be correlated with the two-parameter Hammett equation: log kex = 8.48 - 1.5?+ + 0.77?.For cases where the rate of exciplex formation is slow, the usual homolytic carbon-oxygen bond cleavage occurs from the excited singlet state.The eventual products result from the ion pair since the rate of electron transfer in the radical pair to form the ion pair is considerably faster than the rate of decarboxylation of the benzoyloxy radical.
Rates of decarboxylation of acyloxy radicals formed in the photocleavage of substituted 1-naphthylmethyl alkanoates
Hilborn, James W.,Pincock, James A.
, p. 2683 - 2686 (2007/10/02)
Rates of decarboxylation (kCO2R) have been estimated for the acyloxy racicals 7a-f formed in the photolysis of substituted 1-naphthylmethyl 6a-f. These rates are on a mechanism involving initial carbon-oxygen homolytic bond cleavage from the excited singlet state. The products are formed by two competing pathways: electron transfer in the radical pair to give an ion pair and decarboxylation. Measured product yields along with an of the electron-transfer rate (kET) allow calculation of kCO2R as a function of R. The values obtained are the following (R, k (109 s-1)): CH3, 3CH2, 2.0; (CH3)2CH, 6.5; (CH3)3C, 11; PhCH2, 5.0; PhCH2CH2, 2.3.
Generation of Organic Cations from Group 14 Organometallic Compounds via Photoinduced Electron Transfer in the Presence of Cu(II) Salt
Mizuno, Kazuhiko,Yasueda, Masahiro,Otsuji, Yoshio
, p. 229 - 232 (2007/10/02)
Irradiations of acetonitrile-alcohol (3:1) solutions of arylmethyl silanes, germane, or stannanes in the presence of Cu(BF4)2 gave alkyl arylmethyl ethers in good yields via arylmethyl cations, The efficiency of this photoreaction increased in the order of Si- Ge- Sn-compounds.
Substituent effects on homolytic versus heterolytic photocleavage of (1-naphthylmethyl)trimethylammonium chlorides
Foster, B.,Gaillard, B.,Mathur, N.,Pincock, A. L.,Pincock, J. A.,Sehmbey, C.
, p. 1599 - 1607 (2007/10/02)
Singlet escited state rate constants have been measured for both the heterolytic and homolytic photocleavage of 3- and 4-methoxy and 3- and 4-cyano (1-naphthylmethyl)trimethylammonium chlorides, 6-10.The results are interpreted in terms of the meta effect or changes in charge distribution upon excitation and the competition between bond cleavage, electron transfer, and hydrogen atom transfer in the contact pairs resulting from the two types of cleavage.
Homolytic versus heterolytic cleavage for the photochemistry of 1-naphthylmethyl derivatives
Arnold, B.,Donald, L.,Jurgens, A.,Pincock, J. A.
, p. 3140 - 3146 (2007/10/02)
The photochemical cleavage of the 1-naphthylmethyl derivatives, 1-7, has been examined in methanol solvent under both direct and sensitized conditions.The competition between homolytic and heterolytic cleavage as a function of multiplicity and leaving group has been studied in detail.Only substrates 1, 2, 3, and 7 react on sensitization with xanthone but evidence is presented that the resulting reactivity of 1, 2, and 3 may not be triplet energy transfer but rather exciplex formation.A semi-quantitative scale for photofugacities of the leaving groups from the excited singlet states has been established.
Photochemistry of Naphthylmethyl Halides. Direct and Sensitized Paths to Homolytic and Heterolytic Carbon-Halogen Bond Cleavage
Slocum, Gregory H.,Schuster, Gary B.
, p. 2177 - 2185 (2007/10/02)
Photolysis of the 1-(halomethyl)naphthalenes (X=Cl, Br, I) in methanol and in cyclohexane solution was investigated.Direct and sensitized irradiation leads to carbon-halogen bond cleavage.In methanol solution direct irradiation leads to products of carbon-halogen bond heterolysis, i.e. (methoxymethyl)naphthalene, as well as products derived from bond homolysis.In cyclohexane only homolysis products are observed.The mechanism of the photoreactions was probed by laser spectroscopy, sensitization, and quenching techniques.The results indicate that bond cleavage occurs from excited singlet states but not from the lowest triplet state.Also, an exciplex between sensitizers and the (halomethyl)naphthalene also undergoes carbon-halogen bond cleavage.
