Cyclopalladation of enantiopure oxazolines having the prochiral CMe2 moiety at position 2 of the heterocycle

(R)-4-Ethyl-2-(1,1-dimethylpropyl)-2-oxazoline (1) and (S)-4-tert-butyl-2-(1,1-dimethylbutyl)-2-oxazoline (2) were synthesized in two steps from the corresponding enantiopure amino alcohols and acid chlorides in a total yield of 95% and 72%, respectively. (S)-2-(1-Adamantyl-1-methylethyl)-4-isobutyl-2-oxazoline (3) was obtained from adamantyl bromide and l-leucinol in five steps in a total yield of 82%. Reactions of oxazolines 1–3 with Pd(OAc)2 in AcOH or CH2Cl2 followed by treatment with LiCl afforded the corresponding μ-Cl dimeric cyclopalladated complexes 15, 17, and 20 in good yield. Compounds 15, 17, and 20 reacted with PPh3 to furnish the corresponding mononuclear complexes 16, 19, and 21. The 31P NMR spectra of trans(N,P) adducts 16, 19, and 21 contained signals of two diastereomers in a ratio of ca. 1.3:1.

Reactions of Pd(OAc)2 with enantiopure oxazolines 1–3 with the prochiral CMe2 moiety at position 2 of the heterocycle followed by treatment with LiCl and PPh3 resulted in the formation of the corresponding diastereomeric cyclopalladated complexes 16, 19, and 21 with de < 13%.Figure optionsDownload as PowerPoint slide