The NMR properties, photochromism and efficient syntheses of several [e]-annelated dimethyldihydropyrenes
Date
2018-08-07
Authors
Ward, Timothy Robbins
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
A systematic and efficient route to [e]-annelated derivatives of 2,7-di-t-
butyl-trans-10b, 10c-dimethyl-10b,10c-dihydropyrene 34 has been achieved
which provides access to the benzo, naphtho, and anthro derivatives of 34, by
means of a Diels - Alder reaction of an aryne with a furan. Reaction of the
annulyne derived from bromide 50 with furan gave adduct 52 which could be
both deoxygenated to benzo derivative 53 and reacted with tetrazine 54 to yield
the annuleno furan 55 which subsequently with benzyne and 2,3-naphthalyne
yielded adducts which were deoxygenated to naphtho and anthro derivatives 57
and 59. Reaction of the furan 55 with the benzoannulyne derived from 65 gave
the cyclophane fused pyrene 68, while reaction of the annulyne derived from 50
with the bisfuran 62 gave the chrysene bis pyrene 60. These fused
dihydropyrene derivatives are all photochromic, and the photoisomerizations
were studied In each case. Dihydropyrenes 53, 57, 59, and 65 are simple photoswitches,
while 60 and 68 are more complex multiple state switches. In each
case the kinetics of the MOD to DMDHP reaction was followed to obtain the
activation energy, enthalpy, and entropy. It was found that the activation
enthalpies and energies decreased through the series, from the benzo to the
naphtho to the anthro system. This suggested that the transition states for the
MCD to DMDHP reactions were stabilized by resonance with the respective
annelated fragments.
Detailed analysis of the NMR data of all compounds yielded an
experimental aromaticity scale in which δ(Me) or δ(H4) could yield information to
obtain the relative resonance energy of the annelating fragment. Correlations
between methyl and H4 protons were obtained and compared to related
systems.
Description
Keywords
Nuclear magnetic resonance spectroscopy, Aromatic compounds, Synthesis