Synthesis of the Bis-spiroacetal Moiety of Spirolides B and D

Abstract

An enantioselective synthesis of the bis-spiroacetal fragment of spirolides B and D is reported. The carbon framework was constructed via Barbier reaction of dihydropyran 3 with aldehyde 4, followed by a double oxidative radical cyclization to construct the bis-spiroacetal. A silyl-modified Prins cyclization and enantioselective crotylation successfully installed the stereocenters in the cyclization precursor. The initial unsaturated bis-spiroacetals 2a-d underwent equilibration during epoxidation to trans-epoxide 14 that was converted to a tertiary alcohol. [reaction: see text]

Studies Toward the Synthesis of Spirolides: Assembly of the Elaborated E-Ring Fragment

“…In addition to the 6,5,5-dispirotricyclic bis-ketal, which is only partially stabilized by the anomeric effect, the methyl and butenolide substituents on the double bond of the 6,7-membered spiroimine add to other structural attributes that make spirolides formidable synthetic targets. Several studies aimed at the 6,5,5-dispiroketal portion of spirolides have been described,7,8 yet progress to the intricate spiroimine fragment has been extremely limited 9…”

The Prins Reaction: Advances and Applications

“…A novel, stereoselective Prins reaction of the chiral alkylidene morpholinone derivative 152, prepared from (1R,2S)ephedrine and 3-methyl-2-oxobutanoic acid, was employed in the synthesis of (S)-pantolactone (148). Other , -dialkyl -hydroxybutyrolactones (149)(150)(151), analogues of pantolactone, were prepared employing this stereoselective Prins reaction as the key step [51]. However, significant amounts of by-products were formed in the course of the reaction.…”

“…The synthesis of the tetrahydropyran ring of (-)centrolobine (315) was achieved in optically pure form from the corresponding -acetoxy ether by a Prins cyclization protocol using SnBr 4 [149] or InBr 3 [89] as catalyst, the racemic synthesis of this antibiotic being also achieved by condensation of an aldehyde with an allylic alcohol in the presence of trimethylsilyl iodide [90]. The C16-C23 dihydropyran fragment of spirolides B and D 317 was prepared by a Prins cyclization of (2S,4Z)-1-(benzyloxy)-5-(trimethylsilyl)-4-penten-2-ol and 3-bromopropanal acetal catalyzed by indium trichloride [151]. The C16-C23 dihydropyran fragment of spirolides B and D 317 was prepared by a Prins cyclization of (2S,4Z)-1-(benzyloxy)-5-(trimethylsilyl)-4-penten-2-ol and 3-bromopropanal acetal catalyzed by indium trichloride [151].…”

Production of sulfonated polyetheretherketone/polypropylene fibers for photoactive textiles

“…1 The self-cleaning property of a photoactive textile is based on the discoloration of organic stains by reactive radicals. 2 Photocatalytic oxidation (PCO) is an emerging technology in air purification, and is also based on the decomposition of harmful substances. 3 Although several semiconductors have been used as photocatalysts, 4 titanium dioxide (TiO 2 ) has dominated the research because of its low price, high photostability, and safety.…”

“…16 A self-cleaning property is desirable especially in the clothing industry and, therefore, the research has focused on that sector. 2,23,24 However, these products are not largely available yet and they raise health concerns due to the nanoparticles they contain. There are many commercial air purifiers on the market that use photocatalytic oxidation to turn harmful substances, including volatile organic compounds (VOCs), into less harmful compounds such as CO 2 and H 2 O.…”