Compounds of (i-PrO)3 TiX as novel reagents for regioselective oxirane ring opening

Neighboring Effect of Intramolecular Chlorine Atoms on Epoxide Opening Reaction by Chloride Anions

We investigated the diastereoselectivity of ring openings for chloro vinyl epoxides with various chlorination reagents. In the chlorinolysis reactions using vinyl epoxides having an allyl alcohol, inversion:retention ratios varied depending on the chloride sources. In limited cases, the increase in retention ratio was consistent with the intervention of chloronium ions. In contrast, all vinyl epoxides bearing an α,β-unsaturated ester gave only the inversion products. These results suggest the electron-withdrawing property suppressed the chloronium ions.

Stereochemical Revision, Total Synthesis, and Solution State Conformation of the Complex Chlorosulfolipid Mytilipin B

Chlorosulfolipids constitute a structurally intriguing and synthetically challenging class of marine natural products that are isolated from mussels and freshwater algae. The most complex structure from this family of compounds is currently represented by Mytilipin B, isolated in 2002 from culinary mussel Mytilus galloprovincialis, whose initially proposed structure was shown to be incorrect. In this study, we present the synthesis of four diastereomers which allowed the reassignment of eight stereocenters and the stereochemical revision of Mytilipin B, along with the determination of the dominant solution-state conformation.

Catalytic Regio- and Enantioselective Haloazidation of Allylic Alcohols

Herein we report a highly regio- and stereoselective haloazidation of allylic alcohols. This enantioselective reaction uses readily available materials and can be performed on a variety of alkyl-substituted alkenes and can incorporate either bromine or chlorine as the electrophilic halogen component. Both halide and azido groups of the resulting products can be transformed into valuable building blocks with complete stereospecificity. The first example of an enantioselective 1,4-haloazidation of a conjugated diene is reported as well as its application to a concise synthesis of an aza-sugar.

Stereoselective Halogenation in Natural Product Synthesis

At last count, nearly 5000 halogenated natural products have been discovered. In approximately half of these compounds, the carbon atom to which the halogen is bound is sp(3) -hybridized; therefore, there are an enormous number of natural products for which stereocontrolled halogenation must be a critical component of any synthesis strategy. In this Review, we critically discuss the methods and strategies used for stereoselective introduction of halogen atoms in the context of natural product synthesis. Using the successes of the past, we also attempt to identify gaps in our synthesis technology that would aid the synthesis of halogenated natural products, as well as existing methods that have not yet seen application in complex molecule synthesis. The chemistry described herein demonstrates yet again how natural products continue to provide the inspiration for critical advances in chemical synthesis.

Conformational and configurational analysis in the study and synthesis of chlorinated natural products

The first detailed study of the J-based configuration analysis method in chlorinated hydrocarbons and chlorohydrins is presented along with the development of a spectroscopic database that facilitates configurational assignment of these structures. The data are generated through the investigation of model structures in solution by NMR spectroscopic methods and in the solid state by X-ray crystallography. Consequently, complete conformational analysis of trichlorinated hexane-1,2- and -1,3-diols is presented. The investigations in chlorinated systems for the first time attest to the relevance, reliability, and accuracy of the spectroscopic approach in configurational assignment, which had been otherwise developed for polyketides. During the synthesis of the various molecules that constitute the database and exemplify the various possible stereochemical patterns, a number of observations were made that underscore the unique features of these chlorinated systems. Thus, certain diastereomeric subclasses of 4,5-dichloro-2,3-epoxyhexane-1-ols display a propensity to undergo ring-opening reactions at C-3 with concomitant inversion of configuration at the neighboring C-Cl at C4, implicating the intermediacy of chloronium ions. The observations of positional and stereochemical scrambling in polychlorinated hydrocarbons underscore the necessity of a spectroscopic database that enables rapid, reliable configurational assignment of chlorinated natural products and intermediates en route to these.

Synthesis of [4,5-Bis(hydroxymethyl)-1,3-oxathiolan-2-yl]nucleosides as Potential Inhibitors of HIV via Stereospecific Base-Induced Rearrangement of a 2,3-Epoxy Thioacetate(1)

The synthesis of [4,5-bis(hydroxymethyl)-1,3-oxathiolan-2-yl]nucleosides is described. 2,3-Epoxy alcohol 10 was converted in one pot into thioacetate 11. Treatment of 11 under mild alkaline conditions gave thiirane 12 with inversion of configuration at C-2. We also found that thioacetate 11 rearranges into thiirane 14 under mild acidic conditions. This rearrangement reaction was shown by independent synthesis to proceed with net retention of configuration at C-2. We have proposed a tentative mechanism which may explain the results obtained. Opening of thiiranes 12 and 14 followed by deprotection gave (2R,3R)-2-thiothreitol (23) and (2S,3R)-2-thioerythritol (25), respectively. Regioselective silylation of the primary hydroxyl groups of 23 followed by treatment with trimethyl orthoformate gave 2-methoxy-1,3-oxathiolanes 26 and 27. Condensation with silylated bases followed by deprotection and separation of the anomers gave the oxathiolanylnucleosides. Compounds 29-31, 34, and 35 were found to be inactive when tested for inhibition of HIV-1 activity in vitro.