Table 2. Selective 4π and 6π Electrocyclizations of Dienyl Diketones 1^a.

^aReaction conditions: nucleophile (1 equiv) was added to substrate in THF (1 M), and the reaction was monitored by TLC or NMR.

^bProduct is formed by Nazarov cyclization followed by DABCO elimination.

^cTwenty percent of 2H-pyran product 3g was also observed.

^dProduct obtained as an inseparable mixture of diastereoisomers: 1.2:1 dr (2g) and 6:1 dr (2h) as determined by ¹H NMR spectroscopy.