ORGANIC
LETTERS
2011
Vol. 13, No. 23
6264–6267
Photoinduced Electron-Transfer-
Promoted Redox Fragmentation of
N-Alkoxyphthalimides
Maria Zlotorzynska and Glenn M. Sammis*
Chemistry Department, University of British Columbia, 2036 Main Mall, Vancouver,
British Columbia V6T 1Z1, Canada
Received October 12, 2011
ABSTRACT
A new photoinduced electron-transfer-promoted redox fragmentation of N-alkoxyphthalimides has been developed. Mechanistic experiments
have established that this reaction proceeds through a unique concerted intramolecular fragmentation process. This distinctive mechanism
imparts many synthetic advantages, which are highlighted in the redox fragmentation of various heterocyclic substrates.
Despite the prominence of photochemistry in biological
processes, organic photochemistry has traditionally been
limited by the necessity of high-energy UV radiation.1
Recently, there has been a renaissance in visible-light-
mediated photoinduced electron transfer (PET) processes
there has been a rapid expansion in the scope of viable PET
substrates.4,5 Of all the structural motifs that have been
examined, it is noteworthy that there is only one example
of a PET acceptor adjacent to a weak heteroatomꢀ
heteroatom bond.6 This underrepresented substrate class
has great synthetic potential in visible-light-promoted
processes as the latent reactivity of the weak bond may
be released under mild conditions to undergo numerous
fragmentation possibilities or provide ready access to
heteroatom-centered radicals.
photocatalysts.2
2þ
with new applications of Ru(bpy)3
Following seminal reports by MacMillan3 and Yoon,2aꢀc
(1) For reviews on photoredox catalysis, see: (a) Yoon, T. P.; Ischay,
M. A.; Du, J. Nat. Chem. 2010, 2, 527–532. (b) Narayanam, J. M. R.;
Stephenson, C. R. J. Chem. Soc. Rev. 2011, 40, 102–113.
(2) (a) Ischay, M. A.; Anzovino, M. E.; Du, J.; Yoon, T. P. J. Am.
Chem. Soc. 2008, 130, 12886–12887. (b) Du, J.; Yoon, T. P. J. Am. Chem.
Soc. 2009, 131, 14604–14605. (c) Ishay, M. A.; Lu, Z; Yoon, T. P. J. Am.
Chem. Soc. 2010, 132, 8572–8574. (d) Nicewicz, D.; MacMillan,
D. W. C. Science 2008, 322, 77–80.
(3) (a) Nagib, D. A.; Scott, M. E.; MacMillan, D. W. C. J. Am. Chem.
Soc. 2009, 131, 10875–10877.
(4) For selected examples of ruthenium photocatalysts, see: (a)
Narayanam, J. M. R.; Tucker, J. W.; Stephenson, C. R. J. J. Am. Chem.
Soc. 2009, 131, 8756–8757. (b) Tucker, J. W.; Narayanam, J. M. R.;
Krabbe, S. W.; Stephenson, C. R. J. Org. Lett. 2010, 12, 368–371. (c)
Furst, L.; Matsuura, B. S.; Narayanam, J. M. R.; Tucker, J. W.;
Stephenson, C. R. J. Org. Lett. 2010, 12, 3104–3107. (d) Dai, C.;
Narayanam, J. M. R.; Stephenson, C. R. J. Nat. Chem. 2011, 3, 140–
145. (e) Andrews, S. R.; Becker, J. J.; Gagne, M. R. Angew. Chem., Int.
Ed. 2010, 49, 7274–7276. (f) Rueping, M.; Vila, C.; Koenigs, R. M.;
Poscharny, K.; Fabry, D. C. Chem. Commun. 2011, 47, 2360–2362. (g)
Lu, Z.; Shen, M.; Yoon, T. P. J. Am. Chem. Soc. 2011, 133, 1162–1164.
(5) For selected examples of iridium photocatalysts, see: (a) Condie,
Our studies on the visible light photocatalysis of sub-
strates containing weak heteroatomꢀheteroatom bonds
focused on N-alkoxyphthalimide derivatives. While
phthalimides are well-known to undergo a variety of
photoreactions with UV light,7 surprisingly only one phtha-
limide derivative, an N-acyloxyphthalimide, has been studied
(6) (a) Okada, K.; Okamoto, K.; Morita, N.; Okubo, K.; Oda, M.
J. Am. Chem. Soc. 1991, 113, 9401–9402. (b) Okada, K.; Okubo, K.;
Morita, N.; Oda, M. Tetrahedron Lett. 1992, 33, 7377–7380. (c) Okada,
K.; Okubo, K.; Morita, N.; Oda, M. Chem. Lett. 1993, 2021–2024.
(7) For a review on the photochemistry using N-alkylphthalimides,
see: Yoon, U. C.; Mariano, P. S. Acc. Chem. Res. 2001, 34, 523–533.
ꢀ
A. G.; Gonzlez-Gomez, J. C.; Stephenson, C. R. J. J. Am. Chem. Soc.
2010, 132, 1464–1465. (b) Shih, H.-W.; Vander Wal, M. N.; Grange,
R. L.; MacMillan, D. W. C. J. Am. Chem. Soc. 2010, 132, 13600–13603.
(c) Nguyen, J. D.; Tucker, J. W.; Konieczynska, M. D.; Stephenson,
C. R. J. J. Am. Chem. Soc. 2011, 133, 4160–4163. (d) Reference 3.
r
10.1021/ol202740w
Published on Web 11/07/2011
2011 American Chemical Society