Enantioselektive Katalysen, 90[1]. Optisch aktive Stickstoffliganden mit Dendrimer‐Struktur

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Abstract
Enantioselective Catalysis, 90[1]. ‐ Optically Active Nitrogen Ligands with Dendrimeric Structure2‐Pyridinecarboxaldehyde (1) reacts with (1S,2S)‐2‐amino‐1‐phenyl‐1,3‐propanediol (2) to afford a mixture of the Schiff base 3 and the oxazolidines 3a/3a′, 3b/3b′, which was reduced with NaBH4 to yield the optically active 2‐pyridinylmethylamino alcohol 4. Similarly, 8 was synthesized from 2,6‐pyridinedicarboxaldehyde (7). By acylation of the hydroxy and amino groups, compound 4 was expanded to the corresponding ester amides 5 and 6. Boc and cbz protection of the amino group of 2 produced 10 and 19, respectively. The hydroxy groups of 10 were esterified with 4‐(chloromethyl)‐benzoyl chloride (11) and 3,5‐bis(chloromethyl)benzoyl chloride (12) to give 13 and 14. Compound 19 was converted to the diester 21 by treatment with 3,5‐dimethylbenzoyl chloride (20). Substitution of the chloro substituent in 13 and 14 by (1R,2S)‐ephedrine and (1S,2S)‐2‐(benzylamino)‐1‐phenyl‐1,3‐propanediol, respectively, lead to the tertiary amines 15a‐17a. After removal of the N‐protection, the primary amino groups of 17b‐22 were treated with the aldehydes 1, 7, 27, and 35 to give the corresponding aldimine chelate ligands 23‐26, 28‐34, and 36. Starting with L‐N‐boc‐aspartic acid (37) the tripeptide 39 was formed with two equivalents of L‐aspartic acid dimethyl ester hydrochloride (38). After removal of the boc group followed by condensation with salicylaldehyde, imine 40 was generated. (S)‐2‐amino‐1,1,4,4‐tetraphenyl‐1,4‐butanediol (41), derived from L‐aspartic acid, was treated with the aldehydes 27 and 35. The resulting products 42 and 43 in solution formed mixtures of the diastereomeric oxazolidines 42a and 43a as well as the oxazinanes 42b and 43b. The ligands have been tested in the CuI‐catalyzed cyclopropanation of styrene with ethyl diazoacetate.