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Virgil Boekelheide (1919Ц2003) From Alkaloids to Superphane.

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Obituary
Virgil Boekelheide (1919 – 2003):
From Alkaloids to Superphane
Virgil Boekelheide, Professor of Organic Chemistry in the Department of
Chemistry at the University of Oregon,
died in Eugene, Oregon (USA) on
September 24 at the age of 84.
Boekelheide was descended from a
family of German immigrants, who had
emigrated in the
19th century from
Emsland to the
present South Dakota (USA). He
spent his childhood and student
years in the Midwest and completed his PhD in 1943
under the supervision of C. F.
Koelsch at the
University of Minnesota. He was an
instructor at the University of Illinois
from 1943 to 1946, and from there
moved as professor to the University
of Rochester. From 1960 until 1984 he
worked at the University of Oregon,
where he played a leading role in the
development of this institution and
contributed to the establishment of its
scientific reputation. Until the beginning of the 1960s, alkaloid chemistry
remained at the center of Boekelheide5s
research. However, his interests shifted
more and more toward aromatic chemistry, especially after his move to the
West Coast. Again and again he had
come across new and unusual aromatic
and related p systems—tropones, cyclooctatetraenes, cyclazines—in his natural
product work.
By the middle of the 1960s his
reorientation was complete, and Boekelheide reported new aromatic compounds he had made with substituents
inside the p-electron cloud.[1] Aromatic
chemistry experienced unprecedented
progress during that period, almost 100
years after Kekulé had reported his
structure of benzene. New valence isomers of benzene were prepared, the
H>ckel theory had been generally accepted by organic chemists, and new
synthetic methods were developed, particularly in the field of nonbenzenoid
5540
aromatic systems (for example, by Sondheimer for higher annulenes and by
Nozoe and Hafner for tropones and
azulenes). Crucial to these developments was that NMR spectroscopy
now provided a method for recording
“aromaticity” experimentally. However,
an impasse existed at first in the area of
medium-sized rings: The synthesis of
[10]- and [14]annulenes and their derivatives caused difficulties. The breakthrough was made by E. Vogel in the
case of [10]- and by Boekelheide in the
case of [14]annulenes, through an elegant and highly effective trick. They
eliminated the steric interactions between transannular hydrogen atoms inside the ring of these systems, which
were the root of the synthetic problems,
by replacing these atoms with a methano
bridge and an ethano bridge, respectively, to make a 15,16-dihydropyrene system in the latter case.[2]
Bridged aromatic compounds are
now known as cyclophanes. The p
stacking of planar aromatic systems
had been an obvious step to Boekelheide from the start. He used this
approach in the synthesis of his new p
systems through the valence isomerization of [2.2]meta-cyclophanedienes, a
(photochromic) process that enjoys popularity in the development of new photoswitchable systems to this day. From
this point Boekelheide5s research developed in two directions. While he studied
the chemical, electronic, structural, and
theoretical properties of dihydropyrenes
in the broadest sense, often in cooperation with other research groups, he also
started to solve one of the big problems
in phane chemistry—the synthesis of
“superphane”, a compound in which the
two benzene rings are clamped together
by a total of six ethano bridges. This
target molecule was not only aesthetically attractive, on account of its high
symmetry, but was interesting above all
in terms of how closely two p systems, in
this case two benzene rings on top of one
another, could be pushed together, and
what the consequences of forcing them
together would be. Whereas the distance
between the layers in graphite is 3.4 F,
the distance is only 3.1 F between the
decks of [2.2]para-cyclophane. How far
apart would the aromatic rings be in
superphane? Superphane was prepared
through an extremely elegant iterative
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
synthesis, which made use of the Diels –
Alder addition of o-xylylene intermediates. With an interdeck distance of
2.6 F, this compound still holds the
record for p-stacked aromatic systems.[3]
Boekelheide, who for many years
was on the editorial boards of the
Journal of the American Chemical Society, the Journal of Organic Chemistry,
Organic Reactions, and Organic Syntheses, received many awards and honors
for his scientific achievements. He was
invited to give innumerable plenary
lectures, received distinctions from the
chemical societies of many countries,
and was made a member of the National
Academy of Science of the USA. Particularly during his two periods in Germany as a Senior Alexander von Humboldt Fellow he was able to build up and
strengthen contacts with German colleagues and friends. During his first stay
in Karlsruhe from 1974 to 1975 I came to
know him as a modest and friendly
person with a great sense of humor,
always ready to share not only his ideas,
but also his vast experimental knowhow. Our own work in the field of
cyclophanes would not have developed
so rapidly without his help. He was
convinced that good relations between
countries could only be developed
through personal contact between people and made his research group a
meeting place for countless undergraduate and PhD students, postdoctoral
researchers, and colleagues from all over
the world, whom he encouraged and
assisted long after they had left Eugene.
As he got older his generosity shifted
increasingly toward the arts and music.
Having always been fond of classical
music, he became one of the main
patrons of the music and theater scene
in Oregon. Boekelheide will be always
remembered by his friends around the
world as an outstanding experimental
chemist and philanthropist.
Henning Hopf
TU Braunschweig
[1] V. Boekelheide, J. B. Phillips, Proc. Natl.
Acad. Sci. USA 1964, 51, 550.
[2] V. Boekelheide, J. B. Phillips, J. Am. Chem.
Soc. 1967, 89, 1695 – 1704.
[3] Y. Sekine, M. Brown, V. Boekelheide, J.
Am. Chem. Soc. 1979, 101, 3126 – 3127.
Angew. Chem. Int. Ed. 2003, 42, 5540
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