279-18-5Relevant articles and documents
Bromine-magnesium exchange in gem-dibromocyclopropanes using Grignard reagents
Baird, Mark S,Nizovtsev, Alexey V,Bolesov, Ivan G
, p. 1581 - 1593 (2007/10/03)
Reaction of gem-dibromocyclopropanes with ethylmagnesium bromide at ambient temperature leads to very high yields of allenes; when cyclopropylidene-allene ring opening is suppressed, alternative carbenic products are observed, although other reactions compete. When the reactions are carried out at -60°C, a 1-bromo-1-(bromomagnesio)-cyclopropane is formed which may be trapped by a number of electrophiles.
185-nm Photolysis and Pyrolysis of the Spirocyclopropane-Substituted Azoalkanes of 2,3-Diazatricyclo4,9>non-2-ene and Their Denitrogenated Hydrocarbon Products, the Tricyclo2,7>heptanes
Adam, Waldemar,Zang, Gerald
, p. 3315 - 3323 (2007/10/02)
The 185-nm photolysis and pyrolysis of the spirocyclopropane derivatives of the azoalkanes 2,3-diazatricyclo4,9>non-2-ene (1a), 4',5'-diazaspiro(cyclopropane-1,8'-tricyclo3,7>non-4'-ene) (1b), and 4',5'-diazadispiro(cyclopropane-1,2'-tricyclo3,7>non-4'-ene-8',1''-cyclopropane) (1c) and their denitrogenated hydrocarbon derivatives tricyclo2,7>heptane (2a), spiro(cyclopropane-1,3'-tricyclo2,7>heptane (2b), and dispiro(cyclopropane-1,3'-tricyclo2,7>heptane-6',1''-cyclopropane) (2c) were investigated.It was shownthat the 185-nm photochemical behavior of these substrates does not depend on the degree of spirocyclopropane substitution.As common products in the 185-nm photolysis of the azoalkanes 1a-c were obtained the tricycloalkanes 2a-c (major products), the norbornenes 3a-c, the vinylcyclopentenes 5a-c (minor products), and the exo-methylenecyclohexenes 6a-c (traces).In the case of the parent azoalkane 1a additionally bicyclohept-2-ene (4) and bicyclohept-2-ene (7a) were detected.The major products in the photolysis of the tricycloheptanes 2a-c were the vinylcyclopentenes 5a-c, but also the norbornenes 3a-c and the methylenecyclohexenes 6a-c were formed in considerable amounts.Although the norbornenes 3a-c and the bicycloheptene 4a are logical Wagner-Meerwein rearrangement products, attempts to trap the suspected radical-cationic and zwitterionic intermediates with CF3CH2OH failed.Efforts to generate the authentic radical-cationic species by means of photosensitized elctron transfer (PET) by using sensitizers such as cyanoarenes, quinones, and pyrylium salts were unproductive.Vibrationally excited bicyclohepta-2,7-diyls, generated by the pyrolyses of 2a-c, are not precursors to the norbornenes 3a-c because, instead of such rearrangement products, cyclobutane cleavage of the bicyclopentane moiety takes place to afford the isomeric vinylcyclopentenes 5'a-c.Carbene intermediates, produced either from the 1,3-diyl-type species through fragmentation or from the photodenitrogenation of diazoalkanes, which are generated by retro-cleavage of n,?* excited azoalkanes 1a-c, in turn obtained through internal conversion of higher excited states such as 1?,?*, 1n,?*, and Ry, are proposed as the most likely precursors to either the vinylcyclopentenes 5a-c or methylenecyclohexenes 6a-c, respectively.In violation of Kasha's rule, photochemistry directly from the higher states of the azoalkanes 1a-c competes with internal conversion to the lowest excited state, namely the n,?* state, as it was shown by the formation of norbornenes 3a-c.
Dehalogenation of Geminal Dihalocyclopropanes, α,α-Dichlorocyclobutanones, and Haloketones by Means of Magnesium Anthracene*3THF
Bogdanovic, Borislav,Schlichte, Klaus,Westeppe, Uwe
, p. 27 - 32 (2007/10/02)
1,1-Dichloro-2,2,3,3-tetramethylcyclopropane (1a), 7,7-dichloro- and 7,7-dibromonorcarane (1b) react with magnesium anthracene*3THF (2) under stepwise radical reduction to give 9a,b, 11a,b and 10, carbene products 6a,a',b and 7a,b, and the alkylation products 4a,b and 5a,b, respectively.The distribution of the reaction products is strongly dependent upon the substrate and upon the reaction conditions: for instance, 1a in toluene undergoes a highly selective reduction to yield 9a, whereas in THF at low temperature 4a and 5a predominate.The reaction course proposed for the reaction of 1a with 2 is supported by deuteration experiments. α,α-Dichlorocyclobutanones 12a-e can be reduced with 2 to give α-chlorocyclobutanones 13a-e in moderate to good yields; 12d is thereby converted in high purity into endo-13d.The reduction of 2-haloketones 15a-f with 2 in THF to the ketones 16a-f is possible only in low or moderate yields.
185-nm-Photochemie von Olefinen, gespannten Kohlenwasserstoffen und Azoalkanen in Loesung
Adam, Waldemar,Oppenlaender, Thomas
, p. 659 - 670 (2007/10/02)
Die Moeglichkeit, Chromophore, die nur im Vakuum-UV absorbieren, bei 185 nm direkt anzuregen, hat im letzten Jahrzehnt zur Belebung dieses Teilgebiets der Photochemie gefuehrt.Waehrend Reaktionen in der Gasphase bei λ220nm) treten bei 185-nm-Bestrahlung bevorzugt intramolekulare Umlagerungen, Spaltungen und Isomerisierungen auf, waehrend intermolekulare Radikalkupplungen und -abstraktionen sowie Dimerisierungen (?,?*-Anregung) nur geringfuegig konkurrieren.Neben der leicht moeglichen Denitrogenierung photoresistenter ("reluctant") Azoalkane zeichnen sich wichtige Anwendungsgebiete der kurzwelligen Photolyse auch in der Technik (Photolithographie) und der Medizin (193-nm-Laser) ab.Die Erweiterung des Synthesepotentials der 185-nm-Photochemie - bisher auf direkte cis/trans-Isomerisierungen beschraenkt -, ist eine Herausforderung fuer den Chemiker.
Norpinyl-Norbornyl Rearrangements: Bicycloheptane, 4-Methyl- and 6-Methylbicycloheptane Derivatives
Kirmse, Wolfgang,Siegfried, Rainer,Wroblowsky, Heinz-Juergen
, p. 1880 - 1896 (2007/10/02)
Norpinyl-norbornyl rearrangements have been induced by solvolysis of the 2-norpinyl nitrobenzoates 15b, c and by decomposition of norpinane-, 4-methylnorpinane-, and 6-methylnorpinane-2-diazonium ions (19, 49, 64, 65).No fragmentation to monocyclic cations was observed.The yield of norpinyl products was minimal in water (s processes).With 64 and 65, migration of the bridge trans to the leaving group predominated strongly.The rearrangements afforded exo-2- and endo-2-norbornyl products in comparable quantities.The exo/endo rates depended on the nucleophilicity of the solvent but were little effected by methyl substitution at the migrating carbon.We propose the 7-bridged norbornyl cation (21) as the endo-selective intermediate which rearranges to the exo-selective 6-bridged (or rapidly equilibrating) norbornyl cation (22, 23) in competition with solvent capture.Ion-pair collapse (cf. 15b) accentuates the endo-selectivity.However, ion pairing cannot be the only source of endo-2-norbornyl products, as shown by the deamination reactions in water.
PHOTOLYSIS OF THE AZOALKANE 2,3-DIAZATRICYCLO4,9>NON-2-ENE: DIRECT OBSERVATION OF 4-CYCLOHEXENYLDIAZOMETHANE
Adam, Waldemar,Carballeira, Nestor,Gillaspey, William D.
, p. 5473 - 5476 (2007/10/02)
Besides denitrogenation to the tricycloalkane 8, the photolysis of azoalkane 3 affords the diazoalkane 4, which serves as precursor to the minor hydrocarbon products 9, 10 and 11; irradiation of azoalkane 3 with the 333.6 nm line of an 18-W argon ion laser was essential to obtain preparative quantities of diazoalkane 4 for its detection and identification.
