A highly enantioselective asymmetric hydrogenation route to β-(2R,3S)-methyltryptophan

Tetrahedron Letters

Volumn 39, Issue 21, 1998, Pages 3455-3458

  Hoerrner, R Scott ^a   Askin, David ^a   Volante, R P ^a   Reider, Paul J ^a  

^a MERCK RESEARCH LABORATORIES   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

TRYPTOPHAN DERIVATIVE;

ARTICLE; CATALYSIS; CHIRALITY; DRUG CONFORMATION; ENANTIOMER; HYDROGENATION; STEREOCHEMISTRY; SYNTHESIS;

EID: 0001762703     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(98)00604-2     Document Type: Article

References (27)

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12. 2) at 20°C for 24 h. The crude solution was filtered through silica gel (2:1 ethyl acetate/hexane) to remove the catalyst and provide 8 (482 mg, 96% yield, 97 % ee by SFC HPLC 7).
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25. Isomerization (E/Z) of similar vinyl bromides with DABCO has been reported (Coleman, R.S.; Carpenter, A.J. J. Org. Chem. 1993, 58, 4452). Extended treatment (48 h) of the (E)-vinyl bromide 11 with DABCO or tnethylamine in hot dichloroethane did not result in isomerization to 7.
26. The hydrogenation of 15 was carried out at 60°C (benzene) for 24 h with no reaction. The hydrogenation of 15 was attempted under high pressure (1650 psi) for 24 h with no reaction.
27. The preparation of the isomeric N-acetyl-(E)-dehydro-β-methyltryptophan derivative 16 was carried out from the (E)-vinyl bromide 11 under similar Pd-catalyzed Suzuki coupling with the boronic acid 6 in 65% yield. Interestingly, the (E)-dehydro-β-methyltryptophan derivative 16 has also been resistant to the asymmetric hydrogenation conditions.