Tandem conjugate addition by an O-silylcyanohydrin derived carbanion to 5-(1-menthy10xy)-~5~~0~,
followed by reaction with an ammatic aldehyde gives two dktereoisomfxic adducts.
T&se. afford a single product on treatment with tcrrabutylammonium tluolide. Reduction with concomitant removal of the menthyloxy group, followed by acid catalysed cyclisatb gave a homcchiral tetrahydronaphthakne retrolactone which is an interesting sbuctural isomer of pcxlophyllotoxin.
We have previously shown that tandem conjugate addition to (-)-S-(l-menthyloxy)-2(W)furanone (1) by sulphur stabilised c&anions occurs with a high degree of stereoselectivity and that the adducts produced can be converted into homochiral lignans including aryltetralin lactones (e.g. 2).l However, this approach was of limited value for the preparation of compounds having a substituent at the 4-position (e.g. 3) which would be more closely related to the physiologically active podophyllotoxin se+ries.as 1 Arl = piperonyl At-2 = 3,4,Wimethoxyphenyl Scheme 1
2 X=H 3 X=OH
We therefore decided to investigate the addition of the alternative acyl anion equivalent derived from the teMn@dimethylsilylcyanohydrin (4)> This approach has been used previously by Iwawki et al.7 who showed that the anion undergces tandem conjugate addition to butenolide to give adducts (5) which were used to prepare racemic furoftuan lignans.