Facial selectivities of benzofluorenes bearing a carbonyl, an olefin, or a diene group in spiro geometry. π Spiro substituent effects
摘要:
Benzo[b]- and benzo[c]fluorenes bearing a ketone, an olefin, or a diene substituent in spiro geometry were synthesized to characterize the pi facial selectivity, in comparison with that of the sterically biased benzo[a]fluorene system. We found that fully spiro-conjugated dienes show facially selective behaviors as Diels-Alder dienes, the favored direction depending on the aromatic system. This is in sharp contrast to the olefin analogues, which show essentially no preference. (C) 1997 Elsevier Science Ltd. All rights reserved.