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Influence of Ring Annelation on the Mode Selectivity of the Ionized Diazabicycloheptenes and Corresponding Housanes: An ESR and ENDOR Study
Author(s) -
Gerson Fabian,
Şahin Coşkun
Publication year - 2001
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20010613)84:6<1470::aid-hlca1470>3.0.co;2-w
Subject(s) - chemistry , cyclopentane , pyridazine , octane , cyclopropane , heptane , cyclobutane , annulation , medicinal chemistry , ring (chemistry) , photochemistry , stereochemistry , organic chemistry , catalysis
The tricyclic azoalkanes, (1 α ,4 α ,4a α ,7a α )‐4,4a,5,6,7,7a‐hexahydro‐1,4,8,8‐tetramethyl‐1,4‐methano‐1 H ‐cyclopenta[ d ]pyridazine ( 1c ), (1 α ,4 α ,4a α ,6a α )‐4,4a,5,6,6a‐pentahydro‐1,4,7,7‐tetramethyl‐1,4‐methano‐1 H ‐cyclobuta[ d ]pyridazine ( 1d ), (1 α ,4 α ,4a α ,6a α )‐4,4a,6a‐trihydro‐1,4,7,7‐tetramethyl‐1,4‐methano‐1 H ‐cyclobuta[ d ]pyridazine ( 1e ), and (1 α ,4 α ,4a α ,5a α )‐4,4a,5,5a‐tetrahydro‐1,4,6,6‐tetramethyl‐1,4‐methano‐1 H ‐cyclopropa[ d ]pyridazine ( 1f ), as well as the corresponding housanes, the 2,3,3,4‐tetramethyl‐substituted tricyclo[3.3.0.0 2,4 ]octane ( 2c ), tricyclo[3.2.0.0 2,4 ]heptane ( 2d ), and tricyclo[3.2.0.0 2,4 ]hept‐6‐ene ( 2e ), were subjected to γ ‐irradiation in Freon matrices. The reaction products were identified with the use of ESR and, in part, ENDOR spectroscopy. As expected, the strain on the C‐framework increases on going from the cyclopentane‐annelated azoalkanes and housanes ( 1c and 2c ) to those annelated by cyclobutane ( 1d and 2d ), by cyclobutene ( 1e and 2e ), and by cyclopropane ( 1f ). Accordingly, the products obtained from 1c and 2c in all three Freons used, CFCl 3 , CF 3 CCl 3 , and CF 2 ClCFCl 2 , were the radical cations 3c .+ and 2c .+ of 2,3,4,4‐tetramethylbicyclo[3.3.0]oct‐2‐ene and 2,3,3,4‐tetramethylbicyclo[3.3.0]octane‐2,4‐diyl, respectively. In CFCl 3 and CF 3 CCl 3 matrices, 1d and 2d yielded analogous products, namely the radical cations 3d .+ and 2d .+ of 2,3,4,4‐tetramethylbicyclo[3.2.0]hept‐2‐ene and 2,3,3,4‐tetramethylbicyclo[3.2.0]heptane‐2,4‐diyl. The radical cations 3c .+ and 3d .+ and 2c .+ and 2d .+ correspond to their non‐annelated counterparts 3a .+ and 3b .+ , and 2a .+ and 2b .+ generated previously under the same conditions from 2,3‐diazabicyclo[2.2.1]hept‐2‐ene ( 1a ) and bicyclo[2.1.0]pentane ( 2a ), as well as from their 1,4‐dimethyl derivatives ( 1b and 2b ). However, in a CF 2 ClCFCl 2 matrix, both 1d and 2d gave the radical cation 4d .+ of 2,3,3,4‐tetramethylcyclohepta‐1,4‐diene. Starting from 1e and 2e , the radical cations 4e .+ and 4e′ .+ of the isomeric 1,2,7,7‐ and 1,6,7,7‐tetramethylcyclohepta‐1,3,5‐trienes appeared as the corresponding products, while 1f was converted into the radical cation 4f .+ of 1,5,6,6‐tetramethylcyclohexa‐1,4‐diene which readily lost a proton to yield the corresponding cyclohexadienyl radical 4f . . Reaction mechanisms leading to the pertinent radical cations are discussed.