Axial-selective prins cyclizations by solvolysis of alpha-bromo ethers.
Prins cyclizations are intramolecular electrophilic additions of oxocarbenium ions. They lead to tetrahydropyrans with a heteroatom at the 4-position, and usually show moderate-to-high selectivity for equatorial substitution. We have found that Prins cyclizations carried out under specific conditions produce tetrahydropyrans with almost exclusive formation of the axial 4-substituent. TMSBr, AcBr, and TMSI all lead to axial-selective Prins cyclizations with alpha-acetoxy ether substrates in the presence lutidine. The mechanism appears to involve solvolysis of the intermediate alpha-bromo ether rather than specific or Lewis acid-catalyzed rearrangement. The scope of the reaction, the high yields, and the stereoselectivity make this a valuable new method for tetrahydropyran formation.
Jasti
Ramesh
R
Department of Chemistry, University of California, Irvine, Irvine, California 92697-2025, USA.
Vitale
Justin
J
Rychnovsky
Scott D
SD
D000498:Allyl Compounds / Q000737:chemistry; D003500:Cyclization; D004987:Ethers / Q000737:chemistry*; D004988:Ethers, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry; D006842:Hydrocarbons, Brominated / Q000737:chemistry*; D010080:Oxazoles / Q000737:chemistry
D000498:Allyl Compounds; D004987:Ethers; D004988:Ethers, Cyclic; D006842:Hydrocarbons, Brominated; D010080:Oxazoles