Mechanistic and exploratory organic photochemistry. XLIV. The barrelene to semibullvalene transformation. Correlation of excited-state potential energy surfaces with reactivity

Abstract

Y) was treated with a solution of iodine in ether. The course of the reaction was followed by gas chromatography at 65"; results are in Table IY. Iodine decolorization was very rapid, but at 0.5 ml of iodine the color persisted.Reaction with Bromine. A solution of 8.69 mmol of VI in 21.4 ml of isooctane was treated with a solution prepared from 1 ml (18 mmol) of bromine in 100 ml of carbon tetrachloride. After 60 ml had been added, the color of the bromine persisted, indicating that about 10 mmol had reacted. The mixture contained much yellow solid, which was filtered off and washed with isooctane. The solid was dissolved in water and neutralized with sodium bicarbonate.The solution was saturated with potassium sulfate and extracted several times with chloroform. Extracts were combined, dried over Drierite, and evaporated to leave 0.932 g of solid. The crude product contained residual bromide ion (positive test with aqueous silver nitrate). It reduced potassium permanganate solution. Its infrared spectrum showed stretching bands for C=C (1570 cm-I), olefinic C-H (3030 cm-l), and phosphoryl (1200 cm-l).Reaction with Oxygen. The absorbance at 284 mM of a saturated water solution of VI in a quartz cell sealed with wax was measured over a period of 6.5 hr. The log of the absorbance decreased in a roughly linear fashion from 0.1858 to 0.1098. When the stopper was removed from a solution of log A 0.1098, the absorbance dropped much more rapidly and vanished on long standing. Only end absorption was present in the spectrum.Abstract: A photochemical transformation of barrelene was observed, wherein a C s H~ isomer is produced as the major product; cyclooctatetraene was obtained as a minor product. The structure of the CsHs isomer was elucidated as that of bullvalene minus one vinyl bridge, and the compound was named "semibullvalene." The process was demonstrated to proceed cia the triplet of barrelene in a process subsequently shown to be general. The irradiation of semibullvalene afforded cyclooctatetraene. It was found that semibullvalene undergoes degenerate valence tautomerism at a faster rate than any previously studied system. Barrelene was labeled at all vinyl positions with deuterium, leaving only the bridgehead positions still bearing hydrogen. The method developed for deuteration of barrelene involved treatment with lithium N-deuteriocyclohexylamide in N,N-dideuteriocyclohexylamine; the method promises to be generally useful for preparing deuterated compounds. The location of the hydrogen label in the semibullvalene photolysis product was investigated and found to fit one of two reasonable mechanisms. The reaction mechanism was shown to proceed oia a unique bicyclic, allylic, triplet biradical having finite lifetime. The rearrangement was considered from a theoretical viewpoint with the use of three-dimensional Hiickel theory, and the results were used to correlate the excited-state potential energy surface with observed photochemical behavior. nterest in our laboratory has been heavily focused on

Synthetic Aspects of the Di-π-methane Rearrangement

“…“biradical 1”) and electron-withdrawing groups lead to stabilization when so situated. Examples of DPM rearrangements of acyclic, cyclic, and bicyclic 1,4-dienes are collected in Tables −9. ,,,,,9a,−

17

18

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Pyrolysis of 1.3.5.7‐Cyclooctatetraene, Semibullvalene, and 1.5‐Dihydropentalene in Shock Waves and in a Flow System (Part I)

“…We found no SBV using spectroscopic analysis; for the, in general more sensitive, detection by gas chromatography other problems arise in this particular case [9,14].…”

“…The spectrum is characterized by broad bands located near 265, 272, 280, and 290nm, a shoulder in the range 230-240 nm and a strong increase at shorter wavelengths. The latter features are observed also in the UV spectrum of SBV in solution [14]. An IR gas spectrum of a photolysis mixture with SBV is given in Ref.…”

σ, π‐Isomerisierungen von Monohetero‐σ‐bishomobenzol‐Derivaten. Vorläufige Mitteilung

“…15 Min., 90") [2]. Im Gegensatz zum thermisch sehr stabilen trans-Kohlenwasserstoff 6 (X = CH,) [7], sind die iiberbriickten cis-Abkommlinge des Typs vii [9], viii [lo] Wie wir bereits mitgeteilt haben [2], addiert das Gleichgewichtsystem 9a F)r 10a Diazomethan selektiv (G5-70y0) an den Bicyclus 10a zu dem cis-Pyrazolin lla; dessen direkte Photolyse liefert praktisch quantitativ 13a. Mit vergleichbarer Stereoselektivitat setzen sich auch die stabilen Benzoloxide (NMR.-Genauigkeit) 10b,c mit Diazomethan zu den cis-Pyrazolinen 1 lb,c um, deren Reindarstellung aber durch die leichte thermische Stickstoffeliminierung zu 13b,c erschwert wird.…”