Conspectus
We would all like to make or obtain the materials
or products we
want as soon as possible. This is human nature. This is true also
for chemists in the synthesis of organic molecules. All chemists would
like to make their target molecules as soon as possible, particularly
when their interest is in the physical or biological properties of
those molecules.
As demonstrated by today’s COVID-19
(SARS-CoV-2) pandemic,
rapid synthesis is also crucial to enable chemists to deliver effective
therapeutic agents to the community. Several concepts are currently
well-accepted as important for achieving this: atom economy, step
economy, and redox economy. Considering the importance of synthesizing
organic molecules rapidly, I recently proposed adding the concept
of time economy.
In a multisep synthesis, each step has to be
completed within a
short period of time to make the desired molecule rapidly. The development
of rapid reactions is important but also insufficient. After each
step, frequent and repetitive workup operations such as quenching
the reaction, extraction, separation of water and organic phases,
drying the organic phase, filtration, evaporation, and purification
may be required, and the time necessary for these processing operations
must be taken into account. Indeed, some of the most time-consuming
operations in most syntheses are the purification stages.
On
the other hand, one-pot reactions are processes in which several
sequential reactions are conducted in a single reaction vessel, which
avoids the need to purify intermediates. One-pot reactions are a useful
way to shorten the total synthesis time, and the approach generally
leads to an increase in the yield and a reduction in the amount of
chemical waste formed. Thus, I also propose the importance of pot
economy.
On the basis of these concepts of time and pot economy,
we have
accomplished efficient syntheses of several natural products and medicines.
The key to the success of these syntheses is the use of diphenylprolinol
silyl ether as an effective catalyst in a one-pot reaction, in which
it does not disturb the subsequent reactions. Our strategy is (1)
to construct the chiral key skeletons and/or key components of natural
products and medicines directly using organocatalyst-mediated one-pot
reactions and (2) to conduct the subsequent transformations to the
final molecules in a small number of pots utilizing the internal quench
method. By means of this strategy, PGE1 methyl ester, estradiol
methyl ether, and clinprost were synthesized in three, five, and seven
pots, respectively. Furthermore, (−)-oseltamivir, ABT-341,
baclofen, and Corey lactone were synthesized in a single reaction
vessel. Further optimization of the reactions in terms of time economy
allowed (−)-oseltamivir and Corey lactone to be synthesized
within 60 and 152 min, respectively. These syntheses will be highlighted
as case studies. Although the organocatalyst is a key compound in
this Account, pot- and time-economical syntheses can be expanded to
organometallic chemistry and, ind...