A Practical and Highly Chemoselective Hydrogenation of Aldehydes with a Copper Catalyst

Abstract

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

References and Notes

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Our attempt to hydrogenate (-)-4-(prop-1-en-2-yl)cyclo-hexen-1-carbaldehyde [(-)-perilaldehyde] at S/C = 500
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<A NAME="RU00709ST-10">10</A>

Representative 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).