Enantioselective carboxylation of α-methoxybenzyllithium generated via asymmetric lithiation with a t-BuLi/chiral bis(oxazoline) complex

Tetrahedron Letters

Volumn 40, Issue 37, 1999, Pages 6809-6812

  Komine, Nobuyuki ^a   Wang, Lan Fang ^a   Tomooka, Katsuhiko ^a   Nakai, Takeshi ^a  

^a TOKYO INSTITUTE OF TECHNOLOGY   (Japan)

Author keywords

Bis(oxazoline); Carboxylation; Enantioselection; Lithiation

Indexed keywords

ETHER DERIVATIVE; LITHIUM DERIVATIVE; ORGANOLITHIUM COMPOUND; OXAZOLINE DERIVATIVE; PHENYLACETIC ACID DERIVATIVE;

ARTICLE; CARBOXYLATION; CHEMICAL REACTION KINETICS; ENANTIOMER; REACTION ANALYSIS; SYNTHESIS;

EID: 0033543525     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(99)01364-7     Document Type: Article

References (10)

1. Reviews: (a) Beak, P.; Basu, A.; Gallageher, D. J.; Park, Y. S.; Thayumanavan, S. Acc. Chem. Res. 1996, 29, 552-560.
2. (b) Hoppe, D.; Hense, T. Angew. Chem., Int. Ed. Engl. 1997, 36, 2283-2316.
3. Tomooka, K.; Komine, N.; Nakai, T. Tetrahedron Lett. 1998, 39, 5513-5516.
4. Hoppe has reported that the asymmetric lithiation of benzyl N,N-diisopropylcarbamate with s-BuLi/(-)-sparteine in hexane followed by carboxylation provides the acid in 82% ee (unpublished work described in Ref. Ib). In our hands, however, such high % ee could not be reproduced (only 22% ee was observed) apparently due to the complication arising from crystallization of the lithium species as Hoppe has pointed out (Ref. 2b).
5. Ligand A was prepared by the reported method: Denmark, S. E.; Nakajima, N.; Nicaise, O. J.-C. C.; Faucher, A.-M.; Edwards, J. P. J. Org. Chem. 1995, 60, 4884-4892. Ligands B and C were of commercial origin.
6. 3); lit. for (S)-(+)-4b: Barrett, A. G. M.; Rys, D. J. J. Chem. Soc., Perkin Trans, 1 1995, 1009-1017.
7. 3); lit. for (S)-(+)-4b: Barrett, A. G. M.; Rys, D. J. J. Chem. Soc., Perkin Trans, 1 1995, 1009-1017.
8. In these experiments (R)-3a was consistently formed as the major enantiomer (GLC assay).
9. At present, the question cannot definitely be answered which Li-species, (R)- or (S)-2a, forms (R)-3a, because the steric course (retention vs inversion) of the subsequent carboxylation is ambiguous (Ref. 1b). However, we believe that the present carboxylation proceeds with retention of configuration in view of the fact that the opposite sense of enantioselection has been observed in a similar enantioselective [2,3]-Wittig rearrangement of allyloxy benzyl ether which should proceed in a completely invertive fashion (Ref. 2). Moreover, the same sense of enantioselection was observed also in the reactions of Li-species 2a with aldehydes (Tetrahedron Lett. 1999, 40, 6813) which is more likely to proceed with retention of configuration. Thus, the predominately existing Li-species might be (S)-configurated which produces (R)-3a as a major enantiomer.
10. For the definition and its general schematic energy profile, see Ref. 1a.