C2-symmetric Chiral Diol Research Articles

Dibenzofuran-based C2-Symmetric Chiral Diamines: Their Synthesis and Chiral Recognition Properties

The highly enantioselective synthesis of a dibenzofuran-based C2-symmetric chiral diol has been accomplished by the double enantioselective addition of diethylzinc to dibenzo[b,d]furan-4,6-dicarbaldehyde using a chiral 1,4-amino alcohol as a ligand. Among a series of chiral secondary diamines derived from the C2-symmetric chiral diol, the chiral diamine with two pyrenyl groups can effectively separate enantiomeric 1H NMR signals of various racemic acids.

Enantioselective addition of diethylzinc to aromatic aldehydes catalyzed by C2-symmetric chiral diols

• Optically pure C 2 -symmetric diols have been synthesized. • Chiral diols were evaluated in the enantioselective alkylation of aromatic aldehydes. • The ethylation of benzaldehyde and 1-naphthaldehyde was achieved with excellent ees. Optically pure C 2 -symmetric diols have been synthesized with moderate yields in a straightforward manner, and are used as catalysts in the enantioselective alkylation of aromatic aldehydes with diethylzinc. The addition of diethylzinc to benzaldehyde and sterically hindered 1-naphthaldehyde was achieved with excellent enantioselectivities (97–99% ee) under catalysis with (1 R ,2 R )-1,2-bis(3,5-dibromophenyl)-ethane-1,2-diol and (1 R ,2 R )-1,2-bis(3,5-diphenylphenyl)-ethane-1,2-diol.

Catalytic Enantioselective Allyl- and Crotylboration of Aldehydes Using Chiral Diol•SnCl4 Complexes. Optimization, Substrate Scope and Mechanistic Investigations

We report a novel class of C2-symmetric chiral diols derived from the hydrobenzoin skeleton. The combination of these diols with SnCl4 under Yamamoto's concept of Lewis acid assisted Brønsted acidity (LBA catalysis) leads to high levels of asymmetric induction in the allylboration of aldehydes by commercially available allylboronic acid pinacol ester 1a. The corresponding homoallylic alcohol products of synthetically useful aliphatic aldehydes are obtained in excellent yields with up to 98:2 er. This combined acid manifold is also efficient in catalyzing the diastereo- and enantioselective crotylboration of aldehydes, thus providing the propionate units in >95:5 dr and up to 98:2 er. The X-ray crystal structure of the optimal diol x SnCl4 complex, Vivol (4m) x SnCl4, unambiguously shows the Brønsted acidic character of this LBA catalyst and its highly dissymmetrical environment. Further controls have ruled out a possible boron trans-esterification mechanism with the chiral diol and point to LBA catalyst-derived activation of the pinacol allylic boronates 1. Due to slow dissociation of the diol x SnCl4 complex, a small excess of diol is required in order to suppress a competing racemic cycle catalyzed by free SnCl4.

Synthesis of a new C2-symmetric chiral diol: Application to asymmetric allylboration

New C 2-symmetric chiral diol 1b was prepared from diol 3a, by a thionyl chloride mediated double elmination, hydrogenation and deprotection sequence. A comparative study of the asymmetric allylboration of benzaldehyde with the allylboronates 12 and 13 showed 15 and 18 % e.e. respectively in the corresponding homoallylic alcohol 14.