Megumi Mizukami

Alkylation of 4-hydroxyproline ester derivatives. Diastereoselectivity guided by the anomeric effect and π-interaction

Abstract The alkylation of 4-hydroxyproline derivatives 7 and 1 2 with a range of alkylating reagents was examined. The stereoselectivity was found to be dependent on the reagent and the N-protecting group. This was explained by a concept based on the stereoelectronic effect and π-interaction.

Total synthesis and structural revision of sekothrixide.

The first total synthesis of 14-membered macrolide sekothrixide and the originally proposed structure are reported. Seven contiguous asymmetric centers in the side chain were constructed using ring-openings of several kinds of epoxide. Assembly of the left segment and right segment was performed on the basis of the RCM reaction to generate 14-membered lactones having an E-trisubstituted olefin. These synthetic results led to a revision of C4, C6, and C8 stereochemistry in the structure of natural sekothrixide.

Stereoselective Synthesis of the C25−C36 Segment of Arenicolides A and B: Determination of the Configuration of the Trisubstituted Epoxide

Two diastereomeric epoxides 4a and 4b corresponding to the C(25)-C(36) fragment of arenicolides A and B were synthesized in a stereoselective manner involving the Pd(0)-catalyzed stereospecific methoxy substitution reaction of epoxy unsaturated ester 6 with B(OMe)(3) as the key step. Comparison of the (1)H NMR spectra of the synthetic compounds with that of arenicolide A revealed that the configuration of the epoxide in arenicolides A and B is 30R and 31R.

Syntheses of Polycyclic Tetrahydrofurans by Cascade Reactions Consisting of Five-Membered Ring Selective Prins Cyclization and Friedel–Crafts Cyclization

A novel cascade reaction consisting of a five-membered ring selective Prins cyclization and a subsequent Friedel-Crafts cyclization is reported. Treatment of homocinnamyl alcohols and aromatic aldehydes with BF3·OEt2 in CH2Cl2 afforded hydrocyclopentafurans. Also hydrocyclopentafurans underwent the same cascade reaction after its furan ring cleavage upon treatment with BF3·OEt2 at room temperature. Various combinations of hydropentafurans and aromatic aldehydes or indole aldehydes permitted divergent synthesis of diquinane-furans stuck in aromatic rings.