Frank E. McDonald

Group VI Metal-Promoted Endo-Azacyclizations via Alkyne-Derived Metal Vinylidene Carbenes

Abstract The molybdenum-promoted cycloisomerization of terminal alkynes tethered to β-dicarbonyl nucleophiles is described, providing a novel synthesis of 1,1-disubstituted-2-cyclopentenes.

Tungsten carbonyl-induced cyclizations of alkynyl alcohols to dihydropyranylidene carbenes and α-stannyl dihydropyrans

Abstract Reaction of 1-alkyn-5-ols with tetrahydrofuran-tungsten pentacarbonyl induces cyclization to the corresponding tungsten dihydropyranylidene carbenes. These carbenes can be converted into α-stannyl dihydropyrans upon reaction with tributyltin triflate and triethylamine. This strategy provides the first general preparation of six-membered ring oxacarbenes of the group VI metals, and a novel synthesis of α-stannyl dihydropyrans from acyclic compounds.

SYNTHESIS OF PYRANOSE GLYCALS VIA TUNGSTEN AND MOLYBDENUM PENTACARBONYL-INDUCED ALKYNOL CYCLIZATIONS

Abstract The tungsten pentacarbonyl-induced cyclization of an acyclic alkynol substrate bearing protected oxygen and nitrogen functional groups provides the cyclic tungsten oxacarbene, which is readily converted into a pyranose glycal structurally related to the carbohydrate moieties of the pluramycin and vancomycin families of antitumor antibiotics. In addition a molybdenum-catalyzed cycloisomerization procedure provides an alternative route to this pyranose glycal.

Syn-Oxidative cyclizations of trishomoallylic alcohols: Stereoselective and stereospecific synthesis of trans-tetrahydropyranyl alcohols

Abstract Trifluoroacetylperrhenate promotes the hydroxyl-directed syn -oxidative cyclization of trishomoallylic alcohols. The cyclization reaction is highly stereospecific and stereoselective, providing a novel and efficient synthesis of trans -2,6-disubstituted tetrahydropyranyl alcohols.

Synthesis of trans-syn-trans fused bis-pyrans via endo-selective cyclizations of cyclic sulfates

Abstract Acid-catalyzed cyclization of hydroxy-cyclic sulfates occurs with endo -regioselectivity affording bispyran products from substrates in which the nucleophilic hydroxyl and electrophilic cyclic sulfate groups are 1,2- trans -substituted on a cyclic pyran template. This methodology is demonstrated in an enantioselective synthesis of the trans-syn-trans fused AB cyclic ether rings of the brevetoxin natural products.

SEQUENTIAL APPLICATION OF STEREOSELECTIVE SYN-OXIDATION METHODOLOGIES TO NATURAL PRODUCT SYNTHESIS : A POTENTIALLY BIOMIMETIC APPROACH TO THE C12.C21 BISTETRAHYDROFURAN REGION OF MONENSIN

Abstract The preparation of an all-Z-triene corresponding to an acyclic premonensin triene is described. In analogy to the Townsend syn-oxidative cyclization hypothesis for natural product biosynthesis, a sequence of regioselective and enantioselective syn-dihydroxylation of the triene, cis-selective syn-oxidative cyclization of the diol-diene, and trans-selective syn-oxidative cyclization of the remaining hydroxyalkene gives the correct stereochemical pattern corresponding to the C and D ring tetrahydrofurans of monensin.