title: Synthesis of the C20-C32 tetrahydropyran core of the phorboxazoles and the C22 epimer via a stereodivergent Michael reaction.
abstract: A stereoselective synthesis of the C20-C32 tetrahydropyran core of the phorboxazoles has been achieved in only seven steps and in a 31% overall yield. The C22 epimer was also synthesized. The key step was a silyl ether deprotection/oxy-Michael cyclization. When this step was conducted under Brønsted acid conditions, the C20-C32 core was formed with the desired 2,6-cis-stereochemistry. However, when the silyl ether deprotection/oxy-Michael cyclization was conducted under fluoride conditions buffered with acetic acid, the C22 epimer of the core was the sole product.
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom. paul.clarke@york.ac.uk
authors.forename: Paul A
authors.initials: PA
authors.lastname: Clarke
authors.forename: Kristaps
authors.initials: K
authors.lastname: Ermanis
mesh_terms: D002384:Catalysis; D003500:Cyclization; D015394:Molecular Structure; D010080:Oxazoles / Q000138:chemical synthesis* / Q000737:chemistry; D011714:Pyrans / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D010080:Oxazoles; D011714:Pyrans