1. Photocatalysed [4+2] Annulation of N-Cyclobutylanilines with Alkynes
Jean de Dieu Nubundiho*, Philander Smith College, Little Rock, Arkansas
Jiang Wang, Dr. Nan Zheng, University of Arkansas, Fayetteville, Arkansas,
Department of Chemistry and Biochemistry
I. Abstract
The organic reactions mediated by visible light, a clean and inexpensive
energy that cannot be used up, have increasingly received attention from the
chemistry community. During the past five years, a number of organic
reactions have been developed using visible light photoredox catalysis. In
2012, Dr. Zheng’s lab developed the photocatalysed [3+2] annulation of
cyclopropylanilines with alkynes. We became interested in developing an
analogous [4+2] annulation of N-cyclobutylanilines with alkynes because
cyclobutanes have been almost neglected until recently. Some exciting
chemistry involving cyclobutanes has been reported using Lewis acids or
transition metals but not photocatalysts. To examine the proposed [4+2]
annulation reaction, we needed to synthesize 6-(benzyloxy)-N-phenyl- 1, 2-
dihydrocyclobutabenzen-1-amine as our starting material that took seven
steps to prepare from resorcinol. Herein we present the[4+2] annulation of
N-cylobutylaniline with alkynes under visible light photocatalysis.
II. Introduction
Shifting toward the sustainable industry, visible light photochemistry
contributes to the purpose of this idea. This chemistry is green mainly because it
improves the reaction schemes by generating many bonds in one reaction,
minimizing wastes, using less toxic reagents, and most importantly using
abundant visible light. However, most organic compounds cannot absorb
visible light efficiently. A possible solution to this problem involves the use of
visible light photoredox catalysts such as ruthenium (II) or iridium (III)
polypyridyl complexes to funnel visible light energy to organic molecules. The
photoexcited state of these complexes has a lifetime of 600 nanoseconds, which
are long enough for it to accept or donate one electron from/to organic
molecules. This electron transfer process is the foundation of visible light
photoredox catalysis.
Visible light Photoredox Chemistry versus UV Light PhotocChemistry
 Visible light:
• Abundant
• Renewable
• Usable
• Free
UV Light:
• Expensive apparatus
• Requires input of energy
• Incompatible with profit-driven industry
III. Electron Transfer between Amines and Ru2+* or Ir3+*
• Preparation of Starting Material
IV. Photocatalysed [4+2] Annulation of N-Cyclobutylanilines
with Alkynes Mechanism
.The cyclobutylamine was used as a sacrificial electron donor and a substrate
at the same time.
Light used in
Dr. Zheng’s lab
V. Results
Acknowledgement
NIH8P20 GM103429-12, Arkansas INBRE,
University of Arkansas, Department of Chemistry and Biochemistry
VI. Conclusion
Within eight steps we were able to complete [4+2]annulation of 6-
(benzyloxy)-N-phenyl-1,2-dihydrocyclobutabenzen-1-amine despite
some difficulties. For instance, while preparing the starting material
(N-cyclobutylaniline), the precedent compound (ketone) and the
amine have very close polarity, which made it difficult to separate
them using normal phase silica gel chromatography. For that reason
, in order to do [4+2] annulation of N-cyclobtylaniline , the ketone-
amine mixture was used. The future research will include to find out
the use of the compound synthesized.