SUBSTITUENT-DEPENDENT NITRATION OF 9-SUBSTITUTED 9,10-DIHYDRO-9,10-ETHANOANTHRACENES

Mononitration of 9-substituted ethanoanthracenes, bearing Me, Bu(t), F , Br, I, OMe, NO2, CN, CHO or CO(2)Me substituents at the bridgehead c arbon, was found to occur exclusively at the beta-positions of the aro matic ring. The mononitro products were isolated, identified by H-1 n. m.r. spectroscopy, and their relative proportions were estimated by qu antitative g.l.c. and/or by H-1 n.m.r. spectroscopy. For all the above substrates the proportion of nitration at the beta-position meta to t he bridgehead carbon bearing the substituent [to give compounds of the general form (4)] was greater than the proportion of nitration at the corresponding beta-position para to the bridgehead substituent [to gi ve compounds of the general form (3)]. Whilst the preferential nitrati on at the beta-positions of the aromatic rings is consistent with the previously reported nitration of 9,10-dihydro-9,10-ethanoanthracene (2 a) itself, no observations of this preferential meta attack have been made previously. No correlation could be made of this behaviour with a vailable substituent parameters for the widely sterically and electron ically disparate set of substituents used in this study, and the origi n of this preferential attack remains unclear. Dinitration in this sys tem was studied only superficially. The influence of the bridgehead su bstituent together with that of the nitro group already present on one aromatic ring appear to combine with quite unpredictable results in o rienting the position of attack of the incoming nitro group onto the o ther (non-nitrated) aromatic ring.