287929-74-2Relevant academic research and scientific papers
Amino acid-derived hydroxamic acids as chiral ligands in the vanadium catalysed epoxidation
Malkov, Andrei V.,Bourhani, Zainaba,Kocovsky, Pavel
, p. 3194 - 3200 (2007/10/03)
New sulfonamide-derived hydroxamic acids 7-11 have been developed as chiral ligands for the V-catalysed asymmetric epoxidation, showing high reactivity at subzero temperatures and moderate to good enantioselectivity. The strong accelerating effect exhibited by the ligands of this type can be attributed to the sulfonamide functionality. A range of cinnamyl type allylic alcohols were epoxidised with up to 74% ee. The Royal Society of Chemistry 2005.
Enantioselective syntheses of conformationally rigid, highly lipophilic mesityl-substituted amino acids
Medina, Eva,Moyano, Albert,Pericas, Miquel A.,Riera, Antoni
, p. 972 - 988 (2007/10/03)
Three N-Boc-protected amino acids substituted with a mesityl (=2,4,6- trimethylphenyl) group were synthesized in enantiomerically pure form, either by asymmetric epoxidation or by aminohydroxylation as the source of chirality. The 3-mesityloxirane-2-methanol 7, easily available in high enantiomer purity by Sharpless epoxidation, was converted into 3-{[(tert- butoxy)carbonyl]amino}-3-mesitylpropane-1,2-diol 9 by a regio- and stereoselective ring opening with an ammonia equivalent (sodium azide or benzhydrylamine), followed by hydrogenation and in situ treatment with (Boc)2O (Boc=[(tert-butoxy)carbonyl]) (Scheme 3). Oxidative cleavage of the diol fragment in 9 afforded N-[(tert-butoxy)carbonyl]-α-mesitylglycine 1 of >99% ee. This amino acid was also prepared in enantiomerically pure form starting from 2,4,6-trimethylstyrene (11) by a regioselective Sharpless asymmetric aminohydroxylation, followed by a 2,2,6,6-tetramethylpiperidin-1- yloxyl (TEMPO)-catalyzed oxidation (Scheme 4). On the other hand, 1-[(tert- butoxy)carbonyl]-2-{{[(tert-butyl)dimethylsilyl]oxy}methyl}-3- mesitylaziridine 14 was prepared from 9 by a sequence involving selective protection of the primary alcohol (as a silyl ether), activation of the secondary alcohol as a mesylate, and base-induced (NaH) cyclization (Scheme 5). The reductive cleavage of the aziridine ring (H2, Pd/C), followed by alcohol deprotection (Bu4NF/THF) and oxidation (pyridinium dichromate (PDC)/DMF or (TEMPO)/NaClO) provided, in high yield and enantiomeric purity, N-[(tert-butoxy)carbonyl]-β-mesitylalanine 2. Alternatively, the regioselective ring opening of the aziridine ring of 14 with lithium dimethylcuprate, followed by silyl-ether cleavage and oxidation lead to N- [(tert-butoxy)carbonyl]-β-mesityl-β-methylalanine 3. A conformational study of the methyl esters of the N-Boc-protected amino acids 1 and 3 carried out by variable-temperature 1H-NMR and semi-empirical (AM1) calculations shows the strong rotational restriction imposed by the mesityl group.
