Dearomatizing cyclization of arylsulfonylalkoxymethyl lithiums: a route to the podophyllotoxin skeleton.
[reaction: see text] The phenylsulfonyl group promotes the dearomatizing cyclization of tethered organolithiums onto aromatic rings. With an ether tether, the cyclizations create a new tetrahydrofuran ring, and both cyclization and subsequent electrophilic quenches proceed with high levels of diastereoselectivity. The sulfonyl group can be removed from the cyclized products oxidatively or reductively. The dearomatizing cyclization of a naphthyl sulfone was used in the synthesis of a close structural analogue of podophyllotoxin.
Clayden
Jonathan
J
Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, U.K. j.p.clayden@man.ac.uk
Kenworthy
Martin N
MN
Helliwell
Madeleine
M