A Practical and Highly Chemoselective Hydrogenation of Aldehydes with a Copper Catalyst
17 April 2009 (online)
A practical hydrogenation of aldehydes mediated by an inexpensive and easily available base metal, copper, is reported. A copper complex associated with 1,4-bis(diphenylphosphino)butane (DPPB) hydrogenates α,β-unsaturated aldehydes in a highly chemoselective fashion to give allylic alcohols with improved catalytic productivities. The reaction system was also effective for the conversion of simple aldehydes to the corresponding alcohols.
hydrogenation - aldehydes - copper - homogeneous catalysis - chemoselectivity
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References and Notes
Our attempt to hydrogenate (-)-4-(prop-1-en-2-yl)cyclo-hexen-1-carbaldehyde [(-)-perilaldehyde] at
S/C = 500
with the condition described in ref. 6b, resulted in trace conversion. The reaction reportedly completed at S/C = 20, which was reproduced by us.
Procedure (Table 1, Entry 1)
To a 100 mL stainless steel autoclave equipped with a glass inner lining and a Teflon-coated stirring bar were added [Cu(NO3)(PPh3)2] (11.7 mg, 0.018 mmol) and DPPB (7.7 mg, 0.018 mmol). The atmosphere was replaced with N2, and an EtOH solution (0.03 M) of NaOH (6.0 mL, 0.18 mmol) and (E)-2-methyl-3-phenylprop-2-enal (E/Z = 99:1; 1.26 mL, 9.0 mmol) were then added. Hydrogen gas was initially introduced into the autoclave at a pressure of 1.0 MPa before being reduced to 0.1 MPa by carefully releasing the stop valve. After this procedure was repeated three times, H2 was introduced at 5.0 MPa and the solution was stirred at 50 ˚C for 16 h. Silica gel chromatography (Et2O-hexane = 1:1) after removal of the solvent gave (E)-2-methyl-3-phenyl-
prop-2-en-1-ol (1.32 g, 99%, E/Z = 99:1).