Rh-catalyzed isomerization and intramolecular redox reaction of alkynyl ethers affording dihydropyrans and ketoolefins.
When arylmethyl 4-(sulfonyl)-3-butynyl ether and a catalytic amount of Rh(2)(tfa)(4) (tfa = CF(3)CO(2)-) were heated in toluene, 2-aryl-3-(sulfonyl)-5,6-dihydro-2H-pyran was produced in good yield. Ring closure proceeded in a highly regioselective manner, and no isomeric five-membered product was detected. Alternatively, 2-(5-sulfonyl-4-pentynyl)tetrahydrofuran lacking a benzyl substituent afforded a different product, 9-sulfonyl-1-hydroxy-8-nonen-4-one, upon reaction with the same rhodium catalyst at reflux in wet toluene. Both reactions most likely involve cleavage of the C-H bond alpha to ether in the substrate and subsequent intramolecular transfer of the hydrogen atom to sulfonylacetylene, which is supported by experiments using deuterium-labeled starting materials.
Shikanai
Daisuke
D
Department of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259-B-59 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan.
Murase
Hirohiko
H
Hata
Takeshi
T
Urabe
Hirokazu
H
D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry; D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D004987:Ethers / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011714:Pyrans / Q000138:chemical synthesis* / Q000737:chemistry; D012238:Rhodium / Q000737:chemistry*; D013237:Stereoisomerism
D000475:Alkenes; D000480:Alkynes; D004987:Ethers; D011714:Pyrans; D012238:Rhodium