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(36) Branched cinnamyl phosphate 50 slowly isomerizes into
linear cinnamyl phosphate 11 upon standing. However, no isomerizaꢀ
tion of unreacted 50 was observed under the reaction conditions. See
the Supporting Information for details.
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amino esters, see: (a) Bower, J. F.; Jumnah, R.; Williams, A. C.; Wilꢀ
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46
47
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57
58
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(39) Alternative pathways in which BTM 1 reacts with either
glycine ester 57 or intermediate 58 cannot be ruled out. It is also asꢀ
sumed that the reaction does not proceed via direct αꢀallylation of the
ammonium enolate derived from BTM 1 and 57 given the observed
branchedꢀselectivity.
(22) For a seminal example of 4ꢀnitrophenoxide rebound in
NHCꢀcatalysis, see: Kawanaka, Y.; Phillips, E. M.; Scheidt, K. A. J.
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Muzart, J. Eur. J. Org. Chem. 2007, 2007, 3077ꢀ3089. (c) Marvin, C.
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A., Eds.; Elsevier: Amsterdam, 2014, pp 34ꢀ99. (d) Grange, R. L.;
Clizbe, E. A.; Evans, P. A. Synthesis 2016, 48, 2911ꢀ2968.
(25) See the Supporting Information for more details.
(26) Andersen, N. G.; Keay, B. A. Chem. Rev. 2001, 101, 997ꢀ
1030.
(40) An alternative mechanism in which BTM 1 acts as a
Brønsted base catalyzed is ruled out based upon previous mechanistic
studies. See ref 18.
(41) For examples of S•••O interactions as controlling elements
in isothiourea catalysis, see: (a) Birman, V. B.; Li, X.; Han, Z. Org.
Lett. 2007, 9, 37ꢀ40. (b) Liu, P.; Yang, X.; Birman, V. B.; Houk, K.
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M. D.; Cheong, P. H.ꢀY.; Smith, A. D. Chem. Sci. 2016, 7, 6919ꢀ
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(42) For discussions regarding the origin of S•••O interactions,
see: (a) Reid, R. C.; Yau, M.ꢀK.; Singh, R.; Lim, J.; Fairlie, D. P. J.
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S.; Bartberger, M. D.; Pennington, L. D.; Meanwell, N. A. J. Med.
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(27) The relative and absolute configuration of 14 was assigned
1
by comparison of H NMR and HPLC traces of the corresponding
benzylamide with previously synthesized products.
(28) Ronson, T. O.; Carney, J. R.; Whitwood, A. C.; Taylor, R.
J. K.; Fairlamb, I. J. S. Chem. Commun. 2015, 51, 3466ꢀ3469.
(29) N,NꢀDimethyl 4ꢀnitrophenyl ester 13 is most conveniently
prepared, stored, and used as its HCl salt. However, freebase 13 can
also be used, requiring only 1.2 equiv of iꢀPr2NH to give product 14
in 58% yield, 92:8 dr, and 97:3 er.
(30) (a) Zakzeski J.; Bruijnincx P. C. A.; Jongerius A. L.;
Weckhuysen B. M. Chem. Rev. 2010, 110, 3552ꢀ3599. (b) Lancefield
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260ꢀ264.
(31) Attempted epimerization of synꢀ32 (>95:5 dr) with KOtꢀBu
in THF at 60 °C gave a 50:50 mixture of synꢀ and antiꢀ
diastereoisomers (both 97:3 er). Retreatment of the antiꢀ
diastereoisomer (>95:5 dr) with KOtꢀBu in THF at 60 °C also gave a
50:50 mixture of synꢀ and antiꢀ diastereoisomers. This suggests that
the βꢀstereocenter does not influence the facial selectivity of protonaꢀ
tion and that the observed preference for the antiꢀdiastereoisomer in
Brønsted baseꢀcatalyzed processes is a consequence of the geometry
adopted in the [2,3]ꢀrearrangement transition state.
(32) BTMꢀcatalyzed [2,3]ꢀrearrangement of isolated N,Nꢀdiallyl
ammonium salts gives chemoselective rearrangement through the
cinnamyl substituent. See ref 17b.
(33) The use of an unsymmetrical NꢀMeꢀNꢀBn glycine ester was
unsuccessful under the previously optimized conditions.
(34) The absolute configuration of the corresponding benzyl
amide of 47 was confirmed by Xꢀray crystallographic analysis. CCDC
1549468 contains the supplementary crystallographic data for this
(43) The research data underpinning this publication can be
found at DOI: http://dx.doi.org/10.17630/1cf1b3d5ꢀ3882ꢀ49a4ꢀb859ꢀ
d24129c022bc
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