ISSN:
0170-2041
Keywords:
Amino acids, dehydro-, chiral
;
Amino acids, nonproteinogenic
;
Michael additions of cuprates
;
a5-Reactivity of doubly unsaturated carbonyl compounds
;
Kinetic d2-versus thermodynamic d4-reactivity of Li dienolates
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Stereoselective Conversions of t-Butyl rac-, (R)-, or (S)-5-Alkylidene-2-t-butyl-3-methyl-4-oxo-1-imidazolidinecarboxylates (Chiral 2,3-Dehydroamino Acid Derivatives) and Preparation of Some Nonproteinogenic Amino AcidsThe reacivity of the alkylidene derivatives 1-11 specified in the title and prepared in two operational steps from commercially available Boc-BMI and aldehydes is investigated. - According to high-field 1H-NMR analysis of the crude products, additions of H—H and D—D (catalytic hydrogenation, products 12-20, of R—H (BF3-activated R2CuLi/LiI and protonation, products 21-29), and of Cl2C (CHCl3/NaOH, products 33, 34) occur with complete selectivity from the face opposite to the t-butyl group. The doubly unsaturated carbonyl derivative 11 reacts with dibutyl cuprate in the δ position, again with formation of a single diastereomer 32, while trifluoroethylidene-Boc-BMI 3a is reduced to the difluoro analogue 30 by this cuprate. - Li dienolates are generated by deprotonation with LDA of the ethylidene (2a) and butylidene compound 4a; subsequent alkylations (with primary and secondary halides, products 35-41) and hydroxyalkylations (with aldehydes, products 42-44) lead to single products of electrophilic attack in the a carbonyl position (C-5 of the imidazolidinone ring) under kinetic control. On the other hand, reaction of the 2a-derived dienolate with benzaldehyde under equilibrating conditions furnishes the four possible (E/R, E/S, Z/R, and Z/S) γ adducts 45-48. - A combination of methods - 1H- and 13C-NMR spectroscopy, NOE measurements, spectroscopic analogies, chemical correlation (with authentic samples or by spectroscopic or optical comparison), and X-ray analysis (Table 1, Figure 1, Schemes 1 and 2) - is used to assign the product configurations and thus the stereochemical course of the reactions. Some unusual amino acids (50-52, 54, 55) are prepared by hydrolysis of the corresponding imidazolidinones.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.1991199101119
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