Photochemical Reaction of Optically Active 2-(1'-Methylallyl)anilines with Methanol

Article abstract of DOI:10.1002/hlca.19800630710

It is shown that (-)-(S)-2-(1'-methylallyl)aniline ((-)-(S)-4) on irradiation in methanol yields (-)-(2S,3R)-2,3-dimethylindoline ((-)-trans-8), (-)-(1'R,2'R)-2-(2'-methoxy-1'-methylpropylaniline ((-)-erythro-9) as well as racemic (1'RS,2'SR)-2-(2'-methoxy-1'-methylpropyl)aniline ((+/-)-threo-9) in 27.1, 36.4 and 15.7percent yield, respectively (see Scheme 3).By deamination and chemical correlation with (+)-(2R,3R)-3-phenyl-2-butanol ((+)-erythro-13; see Scheme 4) it was found that (-)-erythro-9 has the same absolute configuration and optical purity as the starting material (-)-(S)-4.Comparable results are obtained when (-)-(S)-N-methyl-2-(1'-methylallyl)aniline ((-)-(S)-7) is irradiated in methanol, i.e. the optically active indoline (+)-trans-10 and the methanol addition product (-)-erythro-11 along with its racemic threo-isomer are formed (cf.Scheme 3).These findings demonstrate that the methanol addition products arise from stereospecific, methanol-induced ring opening of intermediate, chiral trans-(->(-)-erythro-compounds) and achiral cis-spiro<2.5>octa-4,6-dien-8-imines (->(+/-)-threo-compounds; see Schemes 1 and 2).