Synthesis of the BCD-ring of ciguatoxin 1B using an acetylene cobalt complex and vinylsilane strategy

Synthesis of l-Pyranosides by Hydroboration of Hex-5-enopyranosides Revisited

Extensive study of the diastereoselective synthesis of l-pyranosides utilizing hydroboration of substituted exo-glucals (5-enopyranosides) obtained from d-sugars is presented. On the basis of this study we present the empirical rules describing the reaction stereoselectivity and the correlation between the yield of the l-ido product and the size of protecting groups used. Application of these guidelines revealed that the hydroboration of methyl 2,3-O-methyl-6-deoxy-α-d-xylo-hex-5-enopyranoside resulted in exclusive formation of l-ido product with high yield. This method can be successfully applied to the synthesis of l-iduronic acid being an essential component of anticoagulant drugs with diastereoselectivity superior to previously published protocols.

Acetonation of L-pentoses and 6-deoxy-L-hexoses under kinetic control using heterogeneous acid catalysts

The fibrous polymer-supported sulfonic acid catalyst Smopex-101 H+ proved to be an efficient catalyst for the preparation of O-isopropylidene derivatives from a series of rare sugars. Acetonation of the reducing sugars L-arabinose, L-ribose, L-xylose, L-fucose, and L-rhamnose in N,N-dimethylformamide by 2,2-dimethoxypropane or 2-methoxypropene led to the formation of the kinetically favored di-O- and/or mono-O-isopropylidene derivatives in 46-88% yields. The method consists of a simple experimental procedure which does not require predried solvents or reagents. The catalyst is easily recovered and can be regenerated making the procedure economically viable even for large-scale synthesis.

Total synthesis of ciguatoxin

Something fishy: Ciguatoxin (see structure) is one of the principal toxins involved in ciguatera poisoning and the target of a total synthesis involving the coupling of three segments. The key transformations in this synthesis feature acetylene-dicobalthexacarbonyl complexation.

A relay ring-closing metathesis synthesis of dihydrooxasilines, precursors of (Z)-iodo olefins

A convenient Grubbs II metathesis provides dihydrooxasilines by relay RCM (RRCM). Dihydrooxasilines undergo ring opening to give Z-vinyl silanes. These can then be converted to Z-vinyl iodides. This sequence provides a short, high yield, and convenient route to trisubstituted Z-vinyl iodides, useful intermediates for the preparation of polypropionate antibiotics.

Convergent strategies for the total synthesis of polycyclic ether marine metabolites

Marine polycyclic ether natural products continue to fascinate chemists and biologists due to their exceptionally large and complex molecular architectures and potent and diverse biological activities. Tremendous progress has been made over the past decade toward the total synthesis of marine polycyclic ether natural products. In this area, a convergent strategy for assembling small fragments into an entire molecule always plays a key role in successful total synthesis. This review describes our efforts to develop convergent strategies for the synthesis of polycyclic ethers and their application to the total synthesis of gambierol, gymnocin-A, and brevenal, and to the partial synthesis of the central part of ciguatoxins and the nonacyclic polyether skeleton of gambieric acids.

Selective deprotection of terminal isopropylidene acetals and trityl ethers using HClO4 supported on silica gel

Terminal isopropylidene acetals are selectively cleaved to the corresponding 1,2-diols in good to excellent yields in 6-24 h at room temperature by using the 'HClO4.SiO2' reagent system. Likewise, trityl ethers are readily cleaved to the corresponding alcohols in good to excellent yields within 2-3 h at room temperature. Work-up involves merely filtration of the reagent followed by purification of the crude product.