ZnI2-Catalyzed Diastereoselective [4 + 2] Cycloadditions of β,γ-Unsaturated α-Ketothioesters with Olefins.
The potential of β,γ-unsaturated α-ketothioesters participating in hetero-Diels-Alder reaction has remained unexplored. We report herein the first study of a ZnI2-catalyzed highly diastereoselective inverse electron demand hetero-Diels-Alder reaction of β,γ-unsaturated α-ketothioesters with olefins to access highly substituted 3,4-dihydro-2H-pyrans. All the reactions proceed with cis-selectivity in moderate to excellent yields. Under similar reaction conditions, terminal alkynes undergo direct conjugate 1,4-addition to yield δ,ε-acetylenic α-ketothioesters. Furthermore, the utility of these cycloadducts has been demonstrated by an NBS-MeOH mediated stereospecific efficient access to fully substituted pyran rings. The product bromoethers undergo E2 elimination with DBU, resulting in substituted 3,6-dihydro-2H-pyrans. In addition, the thioester moiety of the products has been used for further transformations, such as amidations and Fukuyama coupling reactions.
†Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India.
Kanchan
K
Mal
Supriya
S
Das
Nakul C
NC
Maiti
†Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India.
Ramalingam
R
Natarajan
†Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India.
Indrajit
I
Das
D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D004952:Esters / Q000737:chemistry*; D007454:Iodides / Q000737:chemistry*; D015394:Molecular Structure; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D017967:Zinc Compounds / Q000737:chemistry*
D000475:Alkenes; D004952:Esters; D007454:Iodides; D013438:Sulfhydryl Compounds; D017967:Zinc Compounds; C029770:zinc iodide