ACS Catalysis
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(3) Selected overview: (a) Wuts, P. G. M. Greene`s Protective
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(4) (a) Edson, J. B.; Spencer, L. P.; Boncella, J. M. Org. Lett.
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(b) Tucker, J. W.; Narayanam, J. M. R.; Shah, P. S.;
Stephenson, C. R. J. Chem. Commun. 2011, 47, 5040–5042.
(6) The most popular o-nitrobenzyl PRPG systems release
reactive by-products such as o-nitroso benzaldehydes and
related compounds.3b
(7) (a) Acc. Chem. Res. 2011, 44, 651–840 (special issue). For
recent examples of bioorthogonal catalysis: (b) Hsu, H.-T.;
Trantow, B. M.; Waymouth, R. M.; Wender, P. A.
Bioconjugate Chem. 2016, 27, 376–382. (c) Bose, S.; Ngo, A.
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(d) Alonso-de Castro, S.; Ruggiero, E.; Ruiz-de-Angulo, A.;
Rezabal; E.: Mareque-Rivas, J. C.; Lopez, X.; López-Gallego,
F.; Salassa, L. Chem. Sci. 2017, 8, 4619–4625 and references
cited therein.
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(16) (a) Release by UV light: ref. 15. (b) Release by strong
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Lett. 2005, 7, 1723–1724. (c) Release by nucleophiles (mostly
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(17) Speckmeier, E.; Padíe, C.; Zeitler, K. Org. Lett. 2015, 17,
4818–4821.
(18) We started our efforts with Dsy-protected acids as we
anticipated increased radical stability of the intermediate
by virtue of the additional α-phenyl substituent would
facilitate the photocatalytic cleavage, however being aware
of its disadvantageous additional stereocenter.
(19) (a) Yorimitsu, H.; Shinokubo, H.; Oshima, K. Synlett 2002,
674–686. (b) Postigo, A.; Nudelman, N. S. Coord. Chem.
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(21) Valente, I. M.; Gonçalves, L. M.; Rodrigues, J. A.
J. Chromatogr. A 2013, 1308, 58–62.
(22) For an in situ reactIR kinetic study, please see Supp.
Information.
(23) (a) Neumann, M.; Füldner, S.; König, B.; Zeitler, K. Angew.
Chem. Int. Ed. 2011, 50, 951–954. (b) Hari, D. P.; König, B.
Chem. Commun. 2014, 50, 6688–6699. (c) for a study on the
pH-dependency of eosin Y, see: Majek, M.; Filace, F.; Jacobi
von Wangelin, A. Beilstein J. Org. Chem. 2014, 10, 981–989.
(24) For
a
recent instructive examples, please see:
a) Boyington, A. J.; Riu, M.-L. Y.; Jui, N. T. J. Am. Chem.
Soc. 2017, 139, 6582–6585; b) Aycock, R. A.; Wang, H.; Jui,
N. T. Chem. Sci. 2017, 8, 3121–3125.
(25) Unlike to conditions with Ir photocatalysts: (a) Kim, H.;
Lee, C. Angew. Chem. Int. Ed. 2012, 51, 12303–12306.
(b) Nguyen, J. D.; D´Amato, E. M.; Narayanam, J. M. R.;
Stephenson, C. R. J. Nat. Chem. 2012, 4, 854–859.
(26) Evaluation by chiral HPLC; for details, please see Supp.
Information.
(27) Examples for a generalization as robustness screening, see:
(a) Collins, K. D.; Glorius, F. Nat. Chem. 2013, 5, 597–601.
(b) Collins, K. D.; Rühling, A.; Lied, Glorius, F. Chem. Eur.
J. 2014, 20, 3800–3805. (c) Collins, K. D.; Rühling, A.;
Glorius, F. Nat. Protoc. 2014, 9, 1348–1353.
(28) For a supplementary screening to assess the performance
of Pac protected hydrocinnamic acid Pac-7, see Supp.
Information.
(29) For conditional details and a graphical overview on the
Dsy/Pac orthogonality, please see Supp. Information.
(30) Jung, M. E.; Lyster, M. A. J. Chem. Soc., Chem. Commun.
1978, 315–316.
(10) Few examples of visible light absorbing PRPGs (> 400 nm)
have been developed, however this conceptually leads to
non-storable synthetic intermediates. Chaudhuri, A.;
Venkatesh, Y.; Behara, K. K.; Singh, N. D. P. Org. Lett. 2017,
19, 1598–1601 and references cited therein.
(11) (a) Banerjee, A.; Falvey, D. E. J. Org. Chem. 1997, 62, 6245–
6251. (b) Banerjee, A.; Lee, K.; Falvey, D. E. Tetrahedron
1999, 55, 12699–12710.
(12) (a) Sundararajan, C.; Falvey, D. E. J. Org. Chem. 2004, 69,
5547–5554. (b) Sundararajan, C.; Falvey, D. E. J. Am. Chem.
Soc. 2005, 127, 8000–8001. (c) Borak, J. B.; Falvey, D. E. J.
Org. Chem. 2009, 74, 3894–3899.
(13) For recent examples of carboxylic acid protection:
(a) Šebej, P.; Wintner, J.; Müller, P.; Slanina, T.; Anshori, J.
A.; Antony, L. A. P.; Klán, P.; Wirz, J. J. Org. Chem. 2013,
78, 1833–1843. (b) Goswami, P. P.; Syed, A.; Beck, C. L.;
Albright, T. R.; Mahoney, K. M.; Unash, R.; Smith, E. A.;
Winter, A. H. J. Am. Chem. Soc. 2015, 137, 3783–3786.
(31) Merzouk, A.; Guibé, F.; Loffet, A. Tetrahedron Lett. 1992, 33,
477–480.
(32) Pac protecting groups are also known to be stable to acidic
hydrolysis, such from HBr/HOAc, HCl or CF3COOH:
(a) Stelakatos, G. C.; Paganou, A.; Zervas, L. J. Chem. Soc. C
1966, 1191–1199. b) ref.16c.
(33) For details, please see Supp. Information.
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