Preparation of Mesoporous Silica-Supported Chiral Amino Alcohols for the Enantioselective Addition of Diethylzinc to Aldehyde and Asymmetric Transfer Hydrogenation to Ketones

Table 2

Asymmetric addition of diethylzinc to aldehydes in the presence of 2^a.

Entry	Ar	Ligand 2	Yield (%)^b	e.e. (%)^c
1	Ph	2a	86	50
2^d	Ph	2a	88	52
3	Ph	2b	75	7
4	Ph	2c	80	6
5^e	Ph	Silica gel-supported 2a	59	25
6	o-MeOC6H4	2a	90 (86)^f	57 (54)^f
7^e	o-MeOC6H4	Silica gel-supported 2a	65	34
8	p-MeC6H4	2a	82	43
9	p-ClC6H4	2a	90	50

Reactions were carried out in hexane at room temperature using 2 equiv. of Et₂Zn unless otherwise noted. Absolute configuration was assigned by the elution order from chiral column. ^bDetermined by GC analysis. ^cDetermined by HPLC analysis using Chiralcel OD-H column (3% of 2-propanol in hexane, 0.5 mL/min). ^d10 mol% of ligand was used. ^eSee [41]. ^fThe catalyst was reused three times.