Highly Felkin-Anh selective Hiyama additions of chiral allylic bromides to aldehydes. Application to the first synthesis of nephromopsinic acid and its enantiomer

The chromium(II)-mediated addition (''Hiyama reaction'') of the chiral allylic bromides 13, 15, 19, 22, 24, and 27 to achiral and chiral aldehydes proceeds with high Felkin-Anh selectivity with respect to the stereocenter at C-gamma in the bromide (Table II). By double stereodifferentiation experiments (Tables III/IV) it was shown that the bromide is the stereodominating component in the addition. The methodology was applied to the first synthesis of nephromopsinic acid (-)-69, found in the lichen species nephromopsis stracheyi, and its enantiomer.