Synthesis of polycyclic indolizine derivatives via one-pot tandem reactions of N-ylides with dichloro substituted α,β-unsaturated carbonyl compounds

Convenient and regioselective syntheses of 1,2-annulated, and 1,2-, 5,6- and 1,2-, 7,8-bisannulated polycyclic indolizine derivatives have been achieved by one-pot tandem reactions of cyclic N-ylides derived from the corresponding N-substituted pyridinium, quinolinium, and isoquinolinium salts 1–3 with dichloro substituted α,β-unsaturated carbonyl compounds 4–7. The reactions of the N-ylides with 2,3-dichloroindenone 4, 3,4-dichlorocoumarin 5, and 4a,6,7,8a-tetrachloro-1,4-methanonaphthalene-5,8-dione 6 proceed by sequential [3+2] cycloaddition and elimination of hydrogen chlorides from the cycloadducts. On the other hand, reactions of the N-ylides with 2,3-dichloro-1,4-naphthoquinone 7 take place via a novel reaction sequence to give the products 15–17.