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Kruiswijk, E.; Deck, J. A., Science of Synthesis, (2009) 40, 838.
Enantioselective organocatalysis is a field of central importance in asymmetric synthesis,[50,51–56] and novel modes of substrate activation are achieved using organic catalysts that now compete with, or even surpass, transition-metal catalysts or biocatalysts. The concept of organocatalysis, which can be defined as the acceleration of chemical reactions with less than a stoichiometric amount of an organic compound that does not contain any metal atom, is not new;[57] indeed, the first example of an enantioselective transformation of this type dates back to 1904.[58] Since then much progress has been made and, for example, the efficient asymmetric synthesis of α-amino acids under phase-transfer conditions is now well-established.[59] Thus, pioneering work using phase-transfer catalysts derived by the N-alkylation of cinchona alkaloids[60] was followed by the first catalytic enantioselective synthesis of amino acids in 1989.[61] In this work the quaternary salts 74 (R1 = H) or 76 (R1 = H), based upon cinchonine and cinchonidine, respectively, are employed to promote the C-alkylation of tert-butyl N-(diphenylmethylene)glycinate (73) with 4-chlorobenzyl bromide. After alkylation, both the imino and ester functions of the product are hydrolyzed to release the amino acid 75 (Scheme 33).[62] While modest enantioselectivities (up to 66% ee) are obtained for alkylations with these catalysts, it is possible in related cases to prepare optically pure higher α-amino acids by recrystallization or by enzymatic resolution of the initial C-alkylated imines. In 1994 an improvement on the first-generation catalysts became possible when it was recognized that the active species in these alkylations is formed by O-alkylation of the hydroxy group of the N-benzylated alkaloid in situ.[63] Indeed, an O-allyl group is shown to be the optimal substituent in a second-generation of enantiocomplementary catalysts 74 (R1 = CH2CH=CH2) and 76 (R1 = CH2CH=CH2) (Scheme 33) and enantioselectivities of up to 81% are obtained using them for the alkylation of certain Schiff bases.
Meeeee 88 Meeeeeeeee ee e Meeeee Meee Meeee Meeeeeeeee Meeee Meeeeee eeee Meeeeeee Meeeeeeee ee Meeeeeeee[88]
M eeeeeee eeeee eeeeeeeeeee ee eeeeeeee eeeeeeeeeee eee eeeeeeee eeeeeeeeeeeeee ee 8888 ee eee eeeeee[88,88] eee eeee eeeeeeeeeeeeeeeeeeee eee ee eeeeeeee eee eeeee eeeeeeeeeee eeeee e eeeee-eeeeeeeeee ee eeeeeeeee 88 eee 88 [eeee eeeeeee e M-(8-eeeeeeeeeee)eeeeee eeeee eee e eeee eeeeeee eeeee] ee 88 eee 88 [eeeeeeeeee eee eeee M-(8-eeeeeee)eeeeee eeee, eee eeee ee eeeee eeeee eeeeee eeee e eeee eeeeeee eeeee] (eee Meeeee 88). Meeeeeeee, eee eeeee eee eeeeeeeee eee eeeeeeee eeeee eeeeeeeeeeee eeeeee–eeeeee eeeee-eeeeeeee eeeeeeeeee eeeee 88% eeeeeee eeeeeeeee eeeeeeeee eee eeeeeee ee eeee eeeeeeeeeee, eeeeeee eee eeeeeeeeeeee eeeeeeeee eee ee eeeeeeee ee eeeeeeeee eeee eee eeeeeee eee ee eee eeeeeeee ee eeeee eeeeeeee eeeeee eeeeeeeee eee eeeeeeeeeeeeeee ee eee eeeeeeeeeee.
Meeeee 88 Meeee-Meeeeeeeee Meeeeeeee Meeee ee Meeeeeee Meeeeeeee
Mee eeeeeee eeeeeeeeeeeeeeeeee eeeeeeee eee eee eeeeeeeeee ee Meeeee eeeee eeee ee eeee-eeeee M-(eeeeeeeeeeeeeeeee)eeeeeeeee (88) eeeeeeeee eee eeeeeeeee 88 ee 88 eee eeeeee 8-eeeeeeeeee ee eeeee(eeeeeeee)eeeeeee ee eee eeeeeeeeee eeeeee ee 88%,[88,88,88] eeeeeee eeeeeeeeeeeeeeeeeeee ee eeee ee 88.8% eee eeeeeeee eeee eee eeee eeeeeee eee eee eeeeeeee 88. Me eeeeeeee, eeee eee eeeeeeee 88 ee eeee ee eeeeeee eee eeeeeeee eeeeeee eeee-eeeee M-(eeeeeeeeeeeeeeeee)eeeeeeeee eee 8-eeeee-8-eeeeeeeeeeee eee eeeeeeeee eeeee 88 ee eeeeeeee ee 88% eeeee, eee eeee ee eeeeeeeeeeeeeeeeee ee 88% (Meeeee 88).[88,88]
Meeeee 88 Meeeeee ee ee Meeeeeeeeeeeeeee α-Meeeeeeeee ee eeee-Meeee M-(Meeeeeeeeeeeeeeee)eeeeeeeee[88,88]
Meeee eeeeeeeee eeeeeeeeeeeeeeee eeeeeeeee eee eeee ee eeeeeee eee ee eeeeeeeeeee eeeeeeee ee eeeee Meeeeeeeeee eeeee, 88 (MMMM) ee 88 (MMMM) (Meeeee 88) ee eeeeeeeeeee eeee eee eeeeeeee 88 ee eee eeeeeeeeeeeeeeee 88.[88] Meeee eeeeeeee[88] eeee eeeeeee eeeeeeeee eee eeeeeeeeee ee eeeee-eeeeeeee eeeeeeeee eeee eee 88% eeeeeee eeeeeeeee eeeeeeeee ee eee eeee eee eeeeeee/eeeeeeeeee ee eee eeeeeee ee eeeeeeee eee eeeeeee eeeeee ee eee eeeeeeeee eeee eeeeeeee ee eeeeeee ee eeeeeeeeeeeeeeeee ee eeeeeeeeeeeeeeeeeee. Mee eeeeeeeeeeeeeeeeeeee eeeeeeee eee eeee eeeeeeeeee ee eeeeeeeeee eeeeee eeee eeeee eeeeeeee eeeeeeeeee, eeee eeeee eeeee eeeeeeeeeeeeee eeeeeeee eee eeee eeeeeeeeee, eeee-eeeeeeeeee eeeeeeee eeeeeeeeee eee eeeeeeee.
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Meeeee 88 Meeeeeeeeee Meeee Meee eee eee Meeeeeeeee ee Meeeeeeeeeeeeee eeeee Meeeeeeeeee Meeeeeeeee[88]
Meeeee eeee eeeee eeeeee eeeeeeeee e eeeee ee eeeeeeeeee eeeeeeee eeeeeeeee eeeeeee eeee eee 8,8′-eee(eeeeeeeeeeeeeeeee)-8,8′-eeeeeeeeee (MMMMM) eeeeee ee eeeeeeeeeee.[88,88–88] Meeee eeeeeeeee eee eeee eeeeee ee eeee eeee eee eeeeeeee-eeeee eeeee, eeeee eee eeeeee eeeeeeeeeee ee Meeeeee eeeeeeeeeee, eee eeeeeeeee eeeeeeeeeeeeeeeeeeee (ee ee 88% ee) eee eeeeeeee eee eee eeeeeeeeeee ee eeee-eeeee M-(eeeeeeeeeeeeeeeee)eeeeeeeee ee eeeeeee eeeeee eeeeeeee eeeee eeee 8 eee% ee eee eeeeeeee eee eeeeeeee eeeee ee 88 eeeeeee ee 8°M. Mee eee ee eeeee eeeeeeeee ee eee eeeeeeeeee Meeeeeee eeeeeeeee ee eeeeeeeee ee eeee eeeeeeeeeeee,[88,88] eee eeeeeeeee eeeeeee eeee eeee eeeeeeeeee ee eeeeeeeee eeeee eeeeeeeeee ee eeeeeee eeeee eeeeeeeeee eeeeeeeee eeee eeeeeee eeeee eeeee-eeeeeeee eeeeeeeeee. Meeee eeeeeee Meeeeee eeeeeeeee,[88] Meeeee–Meeeeeeee–Meeeee eeeeeeeee,[88] Meeee eeeeeeeee,[88] eeeeeeeeeeee eeeeeeee eeeeeeeeeeee eeeeeeeee,[88] Meeeeee eeeeeeeeeeeee,[88–88] eeeee eeeeeeeee,[88,88] eeeeeeeee,[88–888] eeeeeeeee,[888–888] eeeeeeeeeeeeeeeee,[888–888] eee eeeeeeeeeeeeee.[888]
References
[50] | Meeee, M. M.; Meeeee, M., Meeee. Meee., (8888) 888, 8888; Meeee. Meee. Mee. Me., (8888) 88, 8888. |
[51] | Meeeeeee, M.; Meeeeee, M.; Meeee, M., Meee. Mee., (8888) 888, 8888. |
[52] | Meee, M., Mee. Meeee. Meeee., (8888) 888, 8888. |
[53] | Meee, M. M.; Meee, M., Mee. Meee. Mee., (8888) 88, 888. |
[54] | Meeeeeeee, M.; Meöeee, M., Me Meeeeeeeee Meeeeeeeeeeeeee: Meee Meeeeeeeee Meeeeeee ee Meeeeeeeeeee ee Meeeeeeeee Meeeeeeee; Meeee-MMM: Meeeeeee, Meeeeee, (8888). |
[55] | Mečeeeeý, M.; Meeeee, M. M., Meeeeeeeeee, (8888) 88, 888. |
[56] | Meeeeeee, M.; Meeóe, M. M., Meeeeeeeeee: Meeeeeeee, (8888) 88, 8888. |
[57] | Meeee, M. M.; Meeeee, M., Meeee. Meee., (8888) 888, 8888; Meeee. Meee. Mee. Me., (8888) 88, 8888. |
[58] | Meeeeeeee, M., Mee. Meeee. Meee. Mee., (8888) 88, 888. |
[59] | M'Meeeeee, M. M., Meeeeeeeeeee Meee, (8888) 88, 8. |
[60] | Meeeeee, M.-M.; Meeee, M.; Meeeeeeee, M. M. M., M. Me. Meee. Mee., (8888) 888, 888. |
[61] | M'Meeeeee, M. M.; Meeeeee, M. M.; Me, M., M. Me. Meee. Mee., (8888) 888, 8888. |
[62] | Meeeeeeee, M. M.; Meeeeeeee, M. M.; Meeee, M.; M'Meeeeee, M. M., M. Mee. Meee., (8888) 88, 8888. |
[63] | M'Meeeeee, M. M.; Me, M.; Meeeeee, M. M., Meeeeeeeeee, (8888) 88, 8888. |
[64] | Meee, M.; Meeeeeeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[65] | Meeee, M. M.; Me, M.; Mee, M. M., M. Me. Meee. Mee., (8888) 888, 88888. |
[66] | Meee, M.; Meeeee, M.; Meeeeeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[67] | Meee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[68] | Meeee, M. M.; Mee, M. M.; Me, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[69] | M'Meeeeee, M. M.; Meeeeee, M.; Meeeeeeeee, M.; Meeeeeeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[70] | Meeeeeeeee, M.; Máeeee, M.; Meeeee, M. M., Meeeeeeeeee: Meeeeeeee, (8888) 88, 8888. |
[71] | Meeeeeee, M.; Meeeeee, M.; eee ee Meeeeeeee, M.; Meeee Meeeeee, M. M. M.; eee Meeee, M.; Meeóe, M.; Meeeeeeeee, M.; Máeeee, M., Meeeeeeeeee: Meeeeeeee, (8888) 88, 8888. |
[72] | M'Meeeeee, M. M.; Meeeeee, M.; Meeeeee, M. M., Meeeeeeeeee, (8888) 88, 8888. |
[73] | Meee, M.-e.; Meeee, M.-M.; Mee, M.-M.; Mee, M.-M.; Meee, M.-e.; Mee, M. M.; Mee, M.-e., Meeeeeeeeee Meee., (8888) 88, 8888. |
[74] | Meee, M.; Meeeeee, M., M. Mee. Meeee. M: Meee., (8888) 888, 8. |
[75] | Meeeeee, M.; Meeeeeeeee, M.-M.; Meeeee, M., Meeeeeeeeee: Meeeeeeee, (8888) 88, 8888. |
[76] | Mee, M.; Meeeee, M.; Meeeeee, M., M. Me. Meee. Mee., (8888) 888, 8888. |
[77] | Mee, M.; Meeeeeee, M.; Meeeee, M.; Meeeeee, M., M. Me. Meee. Mee., (8888) 888, 8888. |
[78] | Mee, M.; Meeeee, M.; Meeeeee, M., M. Me. Meee. Mee., (8888) 888, 8888. |
[79] | Mee, M.; Meeeeee, M., Mee. Meee. Mee., (8888) 88, 888. |
[80] | Meeeeee, M.; Mee, M.; Meee, M., Meee. Meeeee. (Meeeeeeee), (8888), 8888. |
[81] | Mee, M.; Meeeeee, M.; Meeeeee, M., M. Me. Meee. Mee., (8888) 888, 8888. |
[82] | Mee, M.; Meeeeee, M.; Meeeeeee, M.; Meeeeeee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[83] | Meee, M.; Meeeeeeee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[84] | Meeeeeee, M.; Meee, M.; Meeeeee, M. M.; Meeee, M.; Meeeeeee, M., Meeeeeeeeee, (8888) 88, 888. |
[85] | Meeeeeeeeee, M.; Meeee, M.; Møeeeeeee, M. M., M. Mee. Meee., (8888) 88, 8888. |
[86] | Meee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[87] | Meee, M.; Meeeee, M.; Meeeee, M.; Meeeeee, M., Meeeeeeeeee, (8888) 88, 8888. |
[88] | Meee, M.; Meeeee, M.; Meeeee, M.; Meeeeee, M., Meee. Meeeee. (Meeeeeeee), (8888), 88. |
[89] | Meee, M.; Meeeee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[90] | Meeeeeeee, M. M.; Meeeee, M. M., Meeeeeeeeee, (8888) 88, 8888. |
[91] | Meeee, M. M.; Meeee, M.-M., Meeee. Meee., (8888) 888, 8888; Meeee. Meee. Mee. Me., (8888) 88, 8888. |
[92] | Meeee, M. M.; Meeee, M.-M., Mee. Meee., (8888) 8, 8888. |
[93] | Meee, M.; Meeee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[94] | Meee, M.; Mee, M.; Meeee, M.; Meeeeee, M., Meeeeee, (8888), 8888. |
[95] | Meee, M.; Meeee, M.; Mee, M.; Meeee, M.; Meeeeee, M., Meeeeeeeeee, (8888) 88, 8888. |
[96] | Meeeeeee, M.; Meeeeeeee, M.; Meee, M., Meee. Meeee. Meee., (8888) 88, 8888. |
[97] | Meeeeeeee, M.; Meeeeee, M.; Meeee, M. M.; Meeeee, M. M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[98] | Meee, M.; Mee, M. M.; Meeee, M.-M.; Meee-Möeeee, M. M., Meeeeeeeeee: Meeeeeeee, (8888) 88, 888. |
[99] | Meee, M.; Mee, M. M.; Meeee, M.-M.; Meeee, M.; Meeeeee, M.; Meee-Möeeee, M. M., M. Mee. Meee., (8888) 88, 888. |
[100] | Meeee, M.; Meeeee, M. M.; Meeeeeee, M. M., M. Me. Meee. Mee., (8888) 888, 8888. |
[101] | Meeee, M.; Meee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[102] | ee Meeee, M. M. M.; Meeee, M.; Meeee, M.; Meeeeee, M.; eee eee Mee, M., Meeeeeeeeee: Meeeeeeee, (8888) 8, 8888. |
[103] | Meeee, M. M. M.; Meeee, M. M., Meeee. Meee., (8888) 888, 8888.; Meeee. Meee. Mee. Me., (8888) 88, 8888. |
[104] | Meee, M. M.; Meeeeeee, M. M.; Meeeee, M.; Meeeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[105] | Meeeeeeeee, M.; Meeeeeeee, M. M.; Meeeeeeee, M. M., M. Mee. Meee., (8888) 88, 8888. |
[106] | Meeeeeeee, M. M.; Meeeeeeeee, M., MM 8 888 888 M8, (8888); Meee. Meeee., (8888) 888, 888888. |
[107] | Meee, M.; Meeeeeee, M.; Meeeee, M.; Meeeeee, M., M. Mee. Meee., (8888) 88, 8888. |
[108] | Meee, M.; Meeeeeee, M.; Meeeee, M.; Meeeee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[109] | Meee, M.; Meeeeeee, M.; Meeeee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[110] | Meee, M.; Meeeee, M.; Meeeeeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[111] | Meeee-ee-Meeee, M.; Meee, M. M.; Meeeeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
Meeeeee Meeeeeeeeee
- 8.Meeeee-Meee, (8888) 88/8, 888.
- 8.Meeeee-Meee, (8888) M 88e8, 888.