A Novel Synthesis of 2,3‐Dihydro‐1,3‐­methano‐1H‐indene {(Bicyclo[2.1.1]hexeno)benzene} and Analysis of Its NMR Spectra

Abstract

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 α‐pyrones. The title hydrocarbon 3 was then obtained in two subsequent steps. The AA′MM′ 1H NMR spectrum of 3 was analyzed and simulated, leading to corrections of previously published coupling constants. The 13C NMR signal of the methylene carbon atoms appears at particularly low field (δ = 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 π electron systems. As a result, moieties with (4n + 2) π electrons cause deshieldings, whereas those having 4n π electrons evoke shieldings.

AlCl3-catalyzed [3 + 3] cycloaddition of chalcones and β-enamine ketones (esters): a highly efficient access to multisubstituted cyclohexa-1,3-dienamines

“…In addition, 1,3-cyclohexadiene has also been used successfully as a versatile synthetic intermediate in the preparation of polysubstituted diphenylamines, 21 dihydroquinazolinones 22 and other various compounds. [23][24][25][26] As a consequence, considerable effort has been devoted to the synthesis of these six-membered compounds.…”