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Proximate, syn ‐Periplanar Bisdiazene Skeletons: Syntheses, Structures, Homoconjugate Reactivity and Photochemistry
Author(s) -
Exner Kai,
Fischer Gerhard,
Bahr Nikolaus,
Beckmann Eberhard,
Lugan Meinrad,
Yang Fushun,
Rihs Grety,
Keller Manfred,
Hunkler Dieter,
Knothe Lothar,
Prinzbach Horst
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(200003)2000:5<763::aid-ejoc763>3.0.co;2-a
Subject(s) - chemistry , reactivity (psychology) , stereochemistry , metathesis , cycloaddition , crystallography , organic chemistry , catalysis , polymer , polymerization , medicine , alternative medicine , pathology
Rigid NN/NN (diazene/diazene) systems ( F ) consisting of more or less alkylated DBH and DBO chromophoric units ( 1, 2 , X‐ray structures), with very short π,π distances [ d = 2.849 ( 1a , av.), 2.822 Å ( 2 )] and almost perfect syn ‐periplanar π,π alignments [ω = 168.6 ( 1a ), 174.2° ( 2 )] as well as the more flexible, less “proximate” metathesis isomers ( 3a , c , 27a,c , d >4.6 Å, ω = 90‐100°) have been synthesized. Homoconjugate π,π interaction (in 1 , 2 , not in 3 , 27 ) is deduced from UV spectroscopic measurements [π → π* maxima at 239 (234) nm (sh, 260)], while PE analyses furnished only small interaction parameters ( 1a : <0.3 eV). The potential of the novel syn ‐periplanar NN/NN motif in 1 and 2 for the synthesis of somewhat exotic polyheterocycles has been explored by calculation (B3LYP) as well as experimentally: i.a. kinetically stabilized, all ‐ cis ‐peralkylated tetrazolidines ( 38 , 44 ) and perhydro‐1,2,4,5‐tetrazines ( 41 , 47 ) have become accessible (i.a. via novel azomethine/diazene and azomethine/azomethine cycloadditions). In 1a with its unreactive DBO chromophoric subunits, in the “buttressed” derivatives 1b ‐ d , as well as in the DBH/DBO combination 2 , and likewise in more ‘distant’ 27 (differently from the analogous CC/CC and NN/CC systems), irrespective of the excitation conditions employed (light of λ ≥≥ 280, 254 nm, low temperature matrix irradiation, acetone sensitization) no [2+2]photocycloaddition was observed. Instead exclusively N 2 ‐elimination took place. It is argued that unproductive NN/NN photocycloaddition would have become observable through metathesis isomerization of the respective tetrazetidines.