A New Method for Synthesis of Thioethers from Phenyl N-Sulfonamide

<div>A operationally simple, one-pot for regioselective synthesis of thioether route</div><div>directly from phenyl N-sulfonamide by using inexpensive, easily handled trimethylsilyl iodide</div><div>as reducing agent, acetonitrile as the solvent is described. Further no catalyst or additive are</div><div>required, which avoids contamination from the transition metal catalysts in the products.</div>

A New Method for Synthesis of Thioethers from Phenyl N-Sulfonamide

<div>A operationally simple, one-pot for regioselective synthesis of thioether route</div><div>directly from phenyl N-sulfonamide by using inexpensive, easily handled trimethylsilyl iodide</div><div>as reducing agent, acetonitrile as the solvent is described. Further no catalyst or additive are</div><div>required, which avoids contamination from the transition metal catalysts in the products.</div>

Reactions Catalyzed by 2-Halogenated Azolium Salts: From Halogen-Bond Donors to Brønsted-Acidic Salts

Our research group has developed a variety of organocatalysts, especially bi- and multi-functional hydrogen-bond (HB)-donor catalysts. Since 2013, we have become interested in halogen-bond (XB) interactions in organic synthesis, and we have focused on the development of organocatalysts using XBs. Although it is difficult to develop otherwise inaccessible transformations using XBs as the primary interaction, we found several unique reactions that use XB interactions in combination with co-catalysts such as trimethylsilyl iodide, Proton Sponge, and Schreiner’s thiourea. During the synthesis of various 2-iodoazolium salts that can serve as XB donors, a ‘protonated’ 2-iodoazolium salt (a Brønsted-acidic salt) was unexpectedly obtained instead of the corresponding ‘alkylated’ 2-iodoazolium salt (XB donor). The obtained Brønsted-acidic salt is unprecedentedly effective for the N-glycosylation of amides. This account summarizes our findings in this area to date.1 Introduction2 Organoiodine-Compound-Mediated Semipinacol Rearrangement via C–X Bond Cleavage3 2-Iodoazolium-Salt-Catalyzed Reactions through Halogen Bonding (XB)3.1 TMSI-Co-catalyzed Dehydroxylative Coupling of Alcohols with ­Organosilanes3.2 Base-Co-catalyzed Umpolung Alkylation of Oxindoles with an ­Iodonium(III) Ylide3.3 Thiourea-Co-catalyzed N-Glycofunctionalization of Amides3.4 Thiourea-Co-catalyzed N-α-Glycosylation of Amides4 Catalytic Reactions Using 2-Haloazolium Salts as the Brønsted Acids4.1 N-β-Glycosylation of Amides4.2 N-β-2-Deoxyglycosylation of Amides5 Conclusions

The Dixon Synthesis of Manzamine A

The pentacyclic alkaloid manzamine A 4, isolated from a sponge collected in the Okinawa Sea, displays a range of antibacterial, anticancer, and antimalarial activity. The preparation of 4 reported (J. Am. Chem. Soc. 2012, 134, 17482) by Darren J. Dixon of the University of Oxford showcases the versatility of the nitro group in organic synthesis. The nitro alkene 2 was prepared from the commercial bromide 5. Displacement with acetate followed by Swern oxidation led to the aldehyde 6, which was condensed with nitromethane to give 2. Lactam 1 was an intermediate in Professor Dixon’s synthesis (Org. Highlights May 3, 2010) of (–)-nakadomarin A. Lactam 1 was prepared from the tosylate 7, which was derived from pyroglutamic acid. The addition of 1 to the nitroalkene 2 delivered 3 as the dominant diastereomer of the four that were possible. Mannich condensation with formaldehyde and the amine 12 gave 13. The nitro group of 13 was removed by free radical reduction. Exposure of the reduced product to trimethylsilyl iodide gave, via ionization of the ketal, the primary iodide, which was carried onto the nitro compound 14. Dibal selectively reduced the δ-lactam. Partial reduction of the γ-lactam then gave an intermediate that engaged in Mannich condensation with the nitro-activated methylene to give 15. Although there are many protocols for the conversion of a nitro compound to a ketone, most of those were not compatible with the functional groups of 15. Fortunately, Ti(III) was effective. Ce-mediated addition of the Grignard reagent 16 to the ketone followed by deprotection and protection then delivered the silyl ether 17. Remarkably, the ketone 17 could be deprotonated and carried on to the enol triflate 18 without eliminating the TMSO group. Coupling with the stannane 19 then completed the synthesis of manzamine A 4. One-carbon homologation of 18 led to ircinol A, ircinal A, and methyl ircinate (not illustrated).