Photochemische Olefin‐Aziridin‐Cycloaddition
Abstract: [a] Befriedigende Elementaranalysen liegen vor.[b] In Athanol.
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Cited by 13 publications
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Of two very proximate syn‐periplanar bisdiazenes (1,2) mono‐, di‐, tri‐ and tetra‐N‐oxides were prepared, representing six combinations of the individual NN/NNO/ONNO chromophores. According to DFT calculations (B3LYP/6‐31G*), [2+2]photocycloaddition to the respective oxidized tetrazetidines is significantly to moderately endothermic. The metathesis isomerization of the oxidized tetrazetidines is generally highly exothermic and kinetically increasingly favorable with increasing oxidation state. In practice, four out of the six bichromophoric combinations undergo selectively, in competition with N2 elimination from a DBH unit (13) still partially, metathesis isomerization upon π → π* excitation (monochromatic 254 nm light). In the case of the syn‐NNO/NNO combinations (5/6, 14), the photoaddition is thermally reversed. For a ONNO/NN combination (30), internal electron transfer is responsible for a complex reaction pattern. The preparative value of the metathesis reactions, though, is limited: The metathesis‐derived bis[diazene mono(di)oxides] undergo relatively fast secondary photoreactions, while the tri(tetra)oxides undergo rapid thermal transformations. For the NN/NNO systems (12), of three potential pathways for its metathesis isomerization, the one that takes place via σ‐symmetric intermediates (63, 64) is excluded by virtue of the retention of optical purity in the photometathesis of a highly enriched enantiomer [(−)‐12]. Matrix irradiation experiments (12 K, IR control) with 12 result in the appearance of a kinetically highly labile transient. Supported by DFT calculations it is concluded that in the metathesis reactions, the respective tetrazetidine oxides (increasingly destabilized by interactions between oxygen lone pairs and NNσ* orbitals) function as vibrationally excited transients. That thermal reversion of these transients might be a general, nonproductive competition, is suggested by the experimental verification of a “reversed photometathesis” (51 → 15) and by the generally low rates in product formation upon irradiation. The question remains to be answered why in structurally analogous molecular skeletons, [2+2]photocycloaddition occurs in the CC/NN and variously oxidized NN/NN, and not, however, in the parent NN/NN combinations.
Of two very proximate syn‐periplanar bisdiazenes (1,2) mono‐, di‐, tri‐ and tetra‐N‐oxides were prepared, representing six combinations of the individual NN/NNO/ONNO chromophores. According to DFT calculations (B3LYP/6‐31G*), [2+2]photocycloaddition to the respective oxidized tetrazetidines is significantly to moderately endothermic. The metathesis isomerization of the oxidized tetrazetidines is generally highly exothermic and kinetically increasingly favorable with increasing oxidation state. In practice, four out of the six bichromophoric combinations undergo selectively, in competition with N2 elimination from a DBH unit (13) still partially, metathesis isomerization upon π → π* excitation (monochromatic 254 nm light). In the case of the syn‐NNO/NNO combinations (5/6, 14), the photoaddition is thermally reversed. For a ONNO/NN combination (30), internal electron transfer is responsible for a complex reaction pattern. The preparative value of the metathesis reactions, though, is limited: The metathesis‐derived bis[diazene mono(di)oxides] undergo relatively fast secondary photoreactions, while the tri(tetra)oxides undergo rapid thermal transformations. For the NN/NNO systems (12), of three potential pathways for its metathesis isomerization, the one that takes place via σ‐symmetric intermediates (63, 64) is excluded by virtue of the retention of optical purity in the photometathesis of a highly enriched enantiomer [(−)‐12]. Matrix irradiation experiments (12 K, IR control) with 12 result in the appearance of a kinetically highly labile transient. Supported by DFT calculations it is concluded that in the metathesis reactions, the respective tetrazetidine oxides (increasingly destabilized by interactions between oxygen lone pairs and NNσ* orbitals) function as vibrationally excited transients. That thermal reversion of these transients might be a general, nonproductive competition, is suggested by the experimental verification of a “reversed photometathesis” (51 → 15) and by the generally low rates in product formation upon irradiation. The question remains to be answered why in structurally analogous molecular skeletons, [2+2]photocycloaddition occurs in the CC/NN and variously oxidized NN/NN, and not, however, in the parent NN/NN combinations.
H Die 1.4-und 1.5-Diphenyl-norbornadienester 6a, b und 9a, b sowie einige Dihydroderivate (18, 19) werden synthetisiert. Durch direkfe Lichtanregung erhalt man die entsprechenden Quadricyclane 7a, b und 10a, b, deren thermische Bestandigkeit je nach der Stellung der Phenylreste betrachtlich variiert (Pyrolyseverlauf und angenaherte Halbwertszeiten werden bestimmt). Die durch Aceton sensihilisierte Photolyse von 6a, b liefert die Tricyclo[3.2.0.02J]hepten-Derivate 31 bzw. 25,27. Nach vorliiufigen Befunden ist die Di-x-Methan-Umlagerung auch im Falle von 9a, b bevorzugt. Bei der Umsetzung von 7a, lob mit Acetylendicarbonsatire-dimethylester oder Propiolsaure-methylester werden die I : I -Addukte 33a, b hzw. 38 erhalten. Phenyl Substituted Quadricyclane Esters -Synthesis, Thermolysis, Cycloadditions The 1.4-and I .5-diphenyl substituted norbornadiene esters 6a, b, 9a, b and some dihydro derivatives (18,19) are synthesized. The corresponding quadricyclanes 7a, b, 10a, bare obtained upon direct irradiation. Depending on the position of the phenyl substituents the thermal stability of the quadricyclanes varies considerably; the course of their pyrolysis reaction and approximate half-lives are determined. The sensitized (acetone) photolysis of 6a, b leads to the tricyclo[3.2.0.02.~]heptene derivatives 31 and 25, 27, resp. Judged by preliminary results the di-7r-methane transformation is also the favorite pathway in the case of 9a, b. Cycloaddition reactions between 7a, lob, and dimethyl acetylenedicarboxylate or methyl propiolate yield the 1 : 1 adducts 33a, h and 38. Leichtigkeit und Kichtung thermischer lsomerisierungsreaktionen in tetracyclischen Verbindungen des Typs 2 --in groBer Vielfalt durch [27c + 27c]-Photocycloadditionen aus Norbornadienderivaten 1 zuganglich 2) -werden entscheidend durch die Art der Brucke X bestimmt. Der lsocyclus 2a (R --H)3) sowie alle bisher untersuchten Deri-11 44. Mitteil. in der Reihe J'hotochemische Urnwandlungen"; 43. Mitteil. I M. KIuus und H. Prinzbuch, Angew. Prinzbach und Thyes Jdhrg. 104 vate4) liefern beim Erhitzen unter Spaltung der Bindungen A die Ausgangsdiene zuruck. Die Oxa-(2b)s) u n d Azaheterocyclen (2c)6) hingegen lagern sichfast aus-nahmslos7)In die Heterotropilidene 3b bzw. 3c um, ohne daR sich tricyclische Zwischenprodukte (z. B. 4b, c) nachweisen lieBen Die Erwartung, dd8 in den Methylenquadricyclanen 2d die Methylenfunktion die Allylbindungen B soweit schwachte, um die Thermolyse wie be1 den Heterocyclen 2b, c bevorzugt Jm Sinne voii 2 --f 3 ablaufen zu ldssenso dd8 uber die Sequenz 1 +-2 + 3 also Heptafulvene aus Fulvenen zugdnghch wurden . hat sich nicht bestatigt. Ndch den bisherigen Befunden beurteilt, reicht diese Aktivierung nicht aus, um den energetischen Vorteil einer Spaltung der Dreiring/Vierrmgbindungen A kompensieren zu konnens).In dieser Arbeit 9) gehen wir der Frage nach, ob Phenylsubstituenten in den Positionen 2/4 bzw. 2/6 der Quadricyclanester (2a) die lsomerisierung in die Tropilidenreihe 1 enken. 7) Mit der zusatzlichen Aktivierung der Vierring...
Photochemische [2π + 2σ]‐Cycloadditionen im Tetracyclo[4.3.0.0 2,4 .0 3,7 ]non‐8‐en‐System
Photochemische [2n + 2~1-Cycloadditionen im Tetracyclo[4.3 .O .02~4.03~7]non-S-en-Systern 1) Die durch direkte Lichtanregung ausgeliiste Isomerisierung einiger Tetracycl0[4.3.0.02.4.03~7]non-8-en-llerivate 12 zu den Pentacyclo[4.3.0.0~4.03.a.05.7]nonan-Analogen 16 wird beschrieben. Die Spezifitat dieser formalen [2x -t 2a]-Cycloadditionen ist entscheidend von der Art des Losuiigsmittels abhangig. Durch Pyrolyse des Di-tert-butylperesters 16c laBt sich das Grundsystem 16a zu 50% gewinnen. Die Pentacyclen 16 sind thermisch bestandig und gehen mit ,,bishomodienophilen" Partnern keine Additionen ein. Die Strukturen der bei der Darstellung von 12b aus Norbornadien und Acetylendicarbonsaure-dimethylester isolierten 1 : 4bzw. 2 : 2-Addukte werden als 19 bzw. 21 aufgeklart.Photochemical 12 n + 2 UJ Cycloaddition Reactions in the Tetracycl0[4.3.O.~~~.d.~]non-8-ene System l) The isomerization upon direct photoexcitation of some tetracyclo[4.3.0.02.4.03.~J]non-8-ene derivatives 12 to the pentacyclo[4.3.0.02+'.03.~.Os.?]nonane analogs 16 is described. The specificity of this formal [2n -1 201 cycloaddition reaction is determined by the nature of the solvent. Pyrolysis of the di-tert-butyl perester 16c affords the parent hydrocarbon 16a in 50 % yield. The pentacyclic compounds 16 are thermally very stable and do not add ,,bishomodienophilic" reagents. The structures of two minor 1 :4 and 2:2 adducts obtained in the reaction of norbornadiene with dimethyl acetylenedicarboxylate are isolated and characterized as 19 and 21, respectively. Die iniramolekulare Athylen-Cyclopropan-Photocycloaddition hat sich als wertvolle praparative Methode erwiesenz). Schon die ersten Beispiele 1 --f 2 und 3 --f 4 1) 48. Mitteil. in der Reihe ,,Photochemische Umwandlungen" ; 47. Mitteil.: H. Prinzbach und H.
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