Chemistry Reference
In-Depth Information
cyclisation processes, with the larger alkyne substituent being installed in the position
to the cyclopentenone carbonyl unit and the
exo
-product predominating in all instances.
Despite this, it is worth noting that other workers did not engage in research incorporat-
ing this preparative process, in any appreciable sense, until into the 1980s. The reasons
for this somewhat delayed engagement by the preparative community may well have their
foundations in the only low to moderate cyclopentenone yields delivered in many of the pre-
liminary transformations, coupled with the variety of organometallic by-products formed
within a typical reaction process and from which the desired organic compound had to
be removed and purified. Having stated all of this and following a series of subsequent
enhancements to this general preparative method (
vide infra
), the development and use of
the Pauson-Khand reaction escalated considerably. By way of illustration, a simple Web of
Science
SM
search (using “Khand” as the topic keyword), conducted during the production
of this manuscript,
4
delivered some 1,339 publications with this cyclopentenone forming
technique cited in the paper abstract or keywords. Notably, over 1,300 of these publications
have appeared since 1991 and, to illustrate the level of active and on-going employment
of this cyclisation process, almost 6% of all these cited publications appeared in the year
2010 alone. In addition, this key annulation reaction has been the subject of a number of
review articles.
3, 5
In relation to the use of the term “Khand” in the search process mentioned above and
in a more general sense, it is worth discussing the name of this now widely employed
transformation. As noted above, the cyclopentenone-forming transformation was discov-
ered by Peter L. Pauson and co-workers at the University of Strathclyde in Glasgow. One
of these researchers was Ihsan U. Khand, at this stage a postdoctoral research associate
in Pauson's laboratory. Khand was born in India in 1935 and had moved to Glasgow in
1965, before initiating PhD studies in the Pauson laboratory in 1966. Khand's PhD thesis
described the preparation and use of cationic iron sandwich complexes, and was completed
in 1969, with the degree of PhD award being made in 1970. Thereafter and following a
short period undergoing secondary school teacher training in Glasgow, Khand convinced
Pauson to allow him to return to the laboratory for a one year period as a postdoctoral as-
sociate. It was during this period that the reaction of alkyne-cobalt complexes with alkenes
to form cyclopentenones was discovered. Typical of his generosity and remarkable mod-
esty, Peter Pauson only ever referred to this annulation process in spoken or written word
as “The Khand Reaction”. This can be seen quite clearly in Pauson's 1985
Tetrahedron
review of this annulation protocol,
5a
as well as within all of his publications describing the
development and use of this process. Indeed, it was quite a frustration to Pauson that other
workers had amended the name of this, now world-renowned, transformation to include
his own name. This was most vividly highlighted during the reviewing and acceptance
of Pauson's final paper, in collaboration with our own laboratory; during this process the
reviewers and editors had stipulated that the name of the reaction be changed to that which
was more universally accepted. Accordingly, Pauson insisted that, if we were to do this,
a footnote be inserted. This was duly done and read, “Hitherto one of us has preferred to
use the initially designated name of 'Khand' reaction for this synthetic process; in light
of what has now become common usage and following comments from the referees, we
have subsequently employed the more widely accepted term 'Pauson-Khand' throughout
this paper.”
6
Based on all of this and returning to the search term initially utilised, if one
was to employ “Pauson-Khand”, almost one hundred papers would be missed.
