Scheme 1. Selected natural products with a hydrocarbazole skeleton.Scheme 2. Formal [4+2] cycloaddition between indoles and 3-donorsubstituted cyclobutanones 6. PG= protecting group.

Chiral cyclobutanone which had ethyl l-lactate as a chiral auxiliary at the 3-position reacted with aldehydes to give 2,3-dihydro-4-pyranones in up to 93% ee by combined use of titanium(IV) chloride and tin(II) chloride.

No abstract

Scheme 1. Selected natural products with a hydrocarbazole skeleton.Scheme 2. Formal [4+2] cycloaddition between indoles and 3-donorsubstituted cyclobutanones 6. PG= protecting group.

No abstract