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4274096 
Journal Article 
A Novel Synthesis of 2,3-Dihydro-1,3-methano-1H-indene {(Bicyclo[2.1.1] hexeno)benzene} and Analysis of Its NMR Spectra 
Christl, M; Cohrs, C 
2015 
Yes 
European Journal of Organic Chemistry
ISSN: 1434-193X
EISSN: 1099-0690 
2015 
28 
6315-6323 
English 
WOS:000362747900022 
A new synthesis of 2,3-dihydro-1,3-methano-1H-indene (3) has been designed with bicyclo[2.1.1]hex-2-ene serving as starting material, which was added onto chloro-substituted alpha-pyrones. The title hydrocarbon 3 was then obtained in two subsequent steps. The AA 'MM' H-1 NMR spectrum of 3 was analyzed and simulated, leading to corrections of previously published coupling constants. The C-13 NMR signal of the methylene carbon atoms appears at particularly low field (delta = 63.3 ppm). This finding is discussed together with anomalous low-and high-field absorptions of methylene carbon atoms of cyclobutanes and bridgehead carbon atoms of bicyclo[1.1.0]butanes, the 1,3- and 2,4-positions of which, respectively, are bridged by pi electron systems. As a result, moieties with (4n + 2) pi electrons cause deshieldings, whereas those having 4n pi electrons evoke shieldings. 
Cycloaddition; Elimination; Strained molecules; Fused-ring systems; NMR spectroscopy