Chiral erysodienone

The important point concerning stereochemistry was also considered by Barton et al. (117,118), who pointed out that the conversion of chiral 136 to 130b, thence into chiral erysodienone (as 139), must either involve an... 

Recent results" have shown that only (—)-erysodienone, which has the (5S)-chirality of the natural alkaloids, is a precursor for erythraline (103) and a- and -erythroidine (106). The conversion of (S)-N-norprotosinomenine (100) into (5S)-erysodienone (102), it is apparent, involves, formally at least, an inversion of chirality. However, the chirality of (100) may well be lost in vivo for it was found that the biosynthetic intermediate (101) prepared by chemical reduction from chiral erysodienone underwent very rapid racemization at room temperature. 

The combined results are consistent with the pathway shown in Fig. 10. Key intermediates are the symmetrical intermediate (58) and erysodienone (59). In accord with hypothesis both of these compounds served as intact precursors for erythraline (61). Moreover, only (-)-erysodienone (59) which has the (5S)-chirality of the naturally occurring alkaloids, is involved in bio nthesis. 

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