STEREOSELECTIVE CONVERSIONS OF TERT-BUTYL RAC-5-ALKYLIDENE-2-TERT-BUTYL-3-METHYL-4-OXO-1-IMIDAZOLIDINECARBOXYLATES (R)-5-ALKYLIDENE-2-TERT-BUTYL-3-METHYL-4-OXO-1-IMIDAZOLIDINECARBOXYLATES OR (S)-5-ALKYLIDENE-2-TERT-BUTYL-3-METHYL-4-OXO-1-IMIDAZOLIDINECARBOXYLATES (CHIRAL 2,3-DEHYDROAMINO ACID-DERIVATIVES) AND PREPARATION OF SOME NONPROTEINOGENIC AMINO-ACIDS

The reactivity 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 H-1-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 delta-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 alpha-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) gamma-adducts 45-48. - A combination of methods - H-1- and C-13-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.