New Synthesis of α-Benzoyloxy Aldehydes. Application to the Stereoselective Synthesis of Conjugated (E,E)-Dienoic Esters

Article abstract of DOI:10.1021/jo00345a041

A new synthetic method for the preparation of secondary α-benzoyloxy aldehydes (5a-d) and its use in the stereoselective synthesis of conjugated (E,E)-dienone (14) and dienoic esters (9b, 9c, 11, 15b, and 15c) were studied.Two-phase (benzene-H2O) reaction of RCH2CHXCHO (R=CH3, C3H7, C5H11, C7H15; X=Cl, Br) with sodium benzoate (4) in the presence of a catalytic amount of tetrabutylammonium bromide gave the corresponding α-benzoyloxy aldehydes (5a-d) in moderate yields.Compounds 5a-d were converted to γ-benzoyloxy-α,β-unsaturated carbonyl compounds or esters (7b, 7c, 10, 12, 13b, and 13c) either by the TiCl4/py-catalyzed condensation with malonate or acetoacetate or by the Wittig reaction with Ph3P=CHC(O)CH3 and Ph3P=CHCO2Et.Treatment of these compounds with 5 mol percent of (Ph3P)4Pd in refluxing THF afforded the corresponding conjugated (E,E)-dienones and dienoic esters stereoselectively.The reaction sequence was further extended to the stereoselective synthesis of ethyl (2E,4E,6E)-2,4,6-dodecatrienoate (18) and pellitorine (21).