22630-75-7

Upstream product

• 19446-68-5 spiropentane-5,1'-cyclopropane> 
• 19446-70-9 spirodiazabicyclo<2.2.1>hept-2-ene> 
• 19446-70-9 2,3-diazabicyclo/2.2.1/hept-2-ene-7-spirocyclopropane 

Relevant academic research and scientific papers

1,3-Cyclopentanediyls - Intermediates or Transition States?

The energy well of the singlet diradicals 4a and 6 has been determined by the oxygen trapping technique to be 2.7 and 1.9 kcal/mol, respectively.From the oxygen and temperature dependence of the trapping rate of the diradical 4a activation barriers of 2.2 and 4.9 kcal/mol have been derived for the mutual interconversion of the spin isomers with the triplet being the ground state. Key Words: 1,3-Diradicals, energy well, singlet-triplet splitting / 1,3-Cyclopentanediyls

UV Laser Photochemistry: Triplet Biradical Trapping Efficiencies and Lifetimes

The trapping of triplet 1,3-cyclopentadiyl (1a) and the triplet 1,4-biradical 2-cyclopent-2-enyl (6) with molecular oxygen has been studied quantitatively.The lifetime of 1a has been found to range between 720 and 900 ns and that of 6 between 53 and 94 ns depending on the solvent.The biradical 1a was found to be trapped in essentially quantitative yield with no indication of oxygen-catalyzed intersystem crossing.In contrast, 6 was found to be trapped in 54-79percent yield with the residual biradical quenching being due to oxygen-catalyzed intersystem crossing.These and other biradical trapping data have been correlated with 1,3-biradical geometries and found to be in accord with Salem's rules for spin-orbit coupling in triplet biradicals.

Photochemistry of the Azoalkanes 2,3-Diazabicyclohept-2-ene and Spirodiazabicyclohept-2-ene>: On the Questions of One-Bond vs. Two-Bond Cleavage during the Denitrogenation, Cyclization vs. Rearrangement of the 1,3-Diradicals, and Double Inversion.

The thermolysis and 350-nm and 185-nm photolyses of the azoalkanes 2,3-diazabicyclohept-2-ene (1a) and spirodiazabicyclohept-2-ene> (1b) have been investigated.The exo/endo stereochemistry in the bicyclopentanes 2a,b and in the rearranged olefin 3b was determined by deuteration experiments using 5,6-exo-dideuterioazoalkanes 1a,b-d2.Whereas thermal and direct photochemical (350 nm; n, ?*) denitrogenation of azoalkane 1a-d2 led exclusively (>99percent) to bicyclopentane 2a-d2 with preferential (1.54,2.94) double inversion, the triplet-sensitized photolysis afforded nearly complete stereoequlibration.In 185-nm denitrogenetion an unexpectedly high exo/endo ratio (3.1) for bicyclopentane 2a-d2 was found, besides isomerization to cyclopentene 2a-d2.Similar results were obtained in the denitrogenation of spiroazoalkane 1b-d2, which exhibited exo stereochemical preferences in both photoproducts spiropentane-5,1'-cyclopropane> 2b-d2 and bicyclohept-1-ene 3b-d2.The 350-nm photolysis of azoalkane 1b-d2 gave preferential formation of exo-spirobicyclopentane 2b-d2 and exo-olefin 3b-d2 whereas triplet-sensitized decomposition yielded almost complete loss of stereochemical preference in the olefin 3b-d2.The 185-nm photolysis of azoalkane 1b-d2 showed similar behavior compared with the azoalkane 1a, eg., at high exo/endo ratio in spirobicyclopentane 2b-d2.Also olefin 3b was formed with complete stereoequilibration.These diverse experimental results are discussed in terms of one-bond vs. two-bond cleavage processes leading to the diazenyl diradicals D'?,? and D'?,? in the case of low-energy activation (350-nm photolysis and thermolysis) and 1,3-cyclopentadiyls D?,? and D?,? on high-energy activation (185-nm activation).The relatively high degree of double inversion in the corresponding bicyclopentanes and the formation of rearranged cycloalkenes in the 185-nm photodenitrogenation is presumably a direct consequence of concerted two-bond cleavage via the formation of 1D?,? and zwitterionic states of the 1,3-diradical.A Salem diagram for one-bond and two-bond denitrogenation was most helpful in rationalizing these results mechanistically.

PREPARATIVE UV-LASER PHOTOCHEMISTRY OF THE AZOALKANE SPIRO(2,3-DIAZABICYCLOHEPT-2-ENE-7',1-CYCLOPROPANE): TRAPPING OF THE 1,4-DIRADICAL 2-(3-CYCLOPENTENYL)ETHYL BY MOLECULAR OXYGEN

Photo-extrusion of nitrogen from the azoalkane 1 in the presence of molecular oxygen gave besides the hydrocarbons 3 and 5, the endoperoxide 10 and hydroperoxide 11, the former via trapping of the 1,4-diradical 4 by triplet oxygen, the latter by ene-reaction of hydrocarbon 5 with singlet oxygen.