Organocascade Synthesis of Annulated (Z)-2-Methylenepyrans: Nucleophilic Conjugate Addition of Hydroxycoumarins and Pyranone to Branched Nitro Enynes via Allene Formation/Oxa-Michael Cyclization/Alkene Isomerization Sequence.
An efficient organocatalytic reaction using 1,3-nitro enynes with 4-hydroxycoumarin and 4-hydroxy-6-methyl-2-pyrone to afford pyrano-annulated scaffolds in high yield (up to 88% yield) and excellent stereoselectivities (up to >20:1 dr and >99% ee) is described. The reaction proceeded through sequential conjugate addition, allene formation, intramolecular oxa-Michael 6-endo-dig cyclization and DABCO-catalyzed olefin isomerization. A kinetic profile for isomerization was established. The mechanism for the organocascade reaction was proposed according to requisite computational and mechanistic experimental studies.
Department of Chemistry, National Taiwan Normal University , Taipei 11677, Taiwan R.O.C.
Ramani
R
Gurubrahamam
Department of Chemistry, National Taiwan Normal University , Taipei 11677, Taiwan R.O.C.
Bing-Fong
BF
Gao
Department of Chemistry, National Taiwan Normal University , Taipei 11677, Taiwan R.O.C.
Yan Ming
YM
Chen
Department of Chemistry, National Taiwan Normal University , Taipei 11677, Taiwan R.O.C.
Yu-Te
YT
Chan
Department of Chemistry, National Taiwan Normal University , Taipei 11677, Taiwan R.O.C.
Ming-Kang
MK
Tsai
Department of Chemistry, National Taiwan Normal University , Taipei 11677, Taiwan R.O.C.
Kwunmin
K
Chen