title: Studies of the synthesis of providencin: construction and assembly of two major subunits.
abstract: The "northern" sector of the cembranoid diterpene providencin containing a tetrasubstituted cyclobutane was synthesized from the bis(acetonide) of d-glucose using dicyclopentadienylzirconium(0)-mediated oxygen abstraction from a furanose. Oxidative scission of the vinyl substituent of this cyclobutane gave an aldehyde, which was reacted with an alkynylstannane to provide an allenol. Cyclization of the derived allenone with silver nitrate led to a cyclobutylfuran comprising the northern subunit of providencin. The "southern" sector of the cembranoid skeleton containing a trisubstituted iodoalkene attached to an α-phenylselenyl-γ-lactone was synthesized from (R)-glycidol. Negishi carbometalation-iodination established the (E)-iodoalkene, and addition of the lithio dianion of phenylselenoacetic acid to a tosylate generated the substituted lactone. The two sectors were joined via stannylation of the furan of the northern component followed by Stille cross-coupling of the furylstannane with the iodoalkene of the southern subunit. Linkage of the two segments was also made at C12-C13 of providencin using intermolecular aldol condensation of the enolate from the selenyl lactone of the southern portion with an acetaldehyde appendage on the cyclobutane of the northern sector. Closure of the providencin macrocycle from these conjoined subunits was unsuccessful.
authors.affiliation: Department of Chemistry, Oregon State University , Corvallis, Oregon 97331-4003, United States.
authors.forename: James D
authors.initials: JD
authors.lastname: White
authors.forename: Somnath
authors.initials: S
authors.lastname: Jana
mesh_terms: D003503:Cyclobutanes / Q000737:chemistry*; D004224:Diterpenes / Q000138:chemical synthesis* / Q000737:chemistry; D006847:Hydrocarbons, Iodinated / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry*; D008968:Molecular Conformation
chemical_list: D003503:Cyclobutanes; D004224:Diterpenes; D006847:Hydrocarbons, Iodinated; D007783:Lactones; C478991:providencin