Selective cationic cyclizations with α-pyrones as terminators

Publikations-Art

Zeitschriftenbeitrag (peer-reviewed)

Autoren

Leutbecher, H.; Schmidt, D.; Conrad, J.; Beifuss, U.

Erscheinungsjahr

2007

Veröffentlicht in

Synlett

Verlag

Georg Thieme Verlag

DOI

10.1055/s-2007-986660

Seite (von - bis)

2545-2548

The process of the cationic olefin cyclization of 3-substituted 4-hydroxy-2<i>H</i>-pyran-2-ones I (R = Me, Ph, p-C6H4-OMe) that may produce both trans- and cis-pyrano[4,3-b]chromen-1-ones (II) and trans- and cis-pyrano[2,3-b]chromen-4-ones (III) can be efficiently controlled by properly choosing reagents and reaction conditions. The highly selective formation of trans-II can be achieved with Et₂AlCl as a Lewis acid. Preferred formation of cis-II is obsd. with PTSA under microwave conditions at high temps. PTSA and low temps. produce cis-III in excess.