21 dl-Elaeocarpine及びdl-Isoelaeocarpineの全合成

抄録

Total synthesis of dl-elaeocarpine (I) and dl-isoelaeocarpine (II), having the novel indolizidine skeleton, were accomplished. That is, reaction of the diazoketone (VIIIc) with pyrrole was found to afford the 2-pyrrolylmethyl ketone (IXc). Catalytic hydrogenation of IXc over platinum oxide in acetic acid gave the 2-pyrrolidylmethyl-ketone (XII), in which the carbonyl function was not reduced because of steric hindrance by the bulky ortho substituents. Addition of ethyl acrylate to XII furnished the aminoester (XIII), which was subjected to the Dieckmann condensation to give the diketoindolizidine (XIV). The compound (XIV) was derived to the chromone (XVII) via XV and XVI by the agency of boron tribromide, followed by treatment with boiling methanolic hydrogen chloride. Reduction of XVII with sodium borohydride gave two isomeric alcohol (XVIII) and (XIX). The former was oxidized with chromic trioxide to afford dl-isoelaeocargne, m.p. 75-76°, and the latter gave dl-elaeocarpine, m.p. 81-82°, by the same oxidation procedure. The infrared spectra (in chloroform) and Rf values on tlc of the synthetic products were identical with those of the natural products.