Total Synthesis of (+)-Erysotrine via Asymmetric Diels-Alder Reaction Under Super High Pressure

The first total synthesis of (+)-erysotrine in a chiral form was achieved through application of Diels-Alder reaction of a chiral dioxopyrroline with 1-methoxy-3-trimethylsilyloxybutadiene under a 10 Kbar pressure.An effective synthetic route to erythrinan alkaloids using Diels-Alder reaction of an isoquinolinopyrrolinedione with a 1,3-0-disubstituted butadiene as a key step was reported.2In the present communication, we wish to report the first total synthesis of (+)-erysotrine from an L-DOPA derivative utilizing asymmetric Diels-Alder reaction under super high pressure.The c h i d dienophile, dioxopyrroline (4), was prepared as follows (Scheme 1).Condensation of (S)-3,4-dimethoxyphenylalanine methyl ester hydrochloride (1)3 with methyl chloroformylacetate gave the amide (2),4 mp 95-95S°C, in 97% yield.Treatment of 2 with polyphosphate ester (PPE) at 100 "C for 2 h afforded 3,4 mp 139.5-141°C (98%).Condensation of 3 with oxalyl chloride in EQO-CHzC12 at 0°C gave the pyrrolinedione (4)4 (99%), mp.223-224 "C, carrying a COOMe group at C-5.An X-ray analysis of 4 revealed that ring B of this compound is of half-chair conformation and the methoxycarbonyl group is in axial orientation.