A short and stereoselective synthesis of functionalized pentenomycin derivatives

A common and versatile synthetic route to (-) and (+) pentenomycin I, (+) halopentenomycin I and dehydropentenomycin

A versatile and stereoselective total synthesis of (+) and (-) pentenomycin I, (+) halopentenomycins I and dehydropentenomycin from a common chiral polyhydroxylated cyclopentene through oxidation and protection/deprotection has been described. Stereoselective hydroxymethylation, stereoselective Grignard reaction and ring closing metathesis are the key features of our approach.

2,2,6,6-Tetra-bromo-3,4,4,5-tetra-meth-oxy-cyclo-hexa-none

In the title compound, C₁₀H₁₄Br₄O₅, synthesized from the meth­oxy Schiff base N-(pyridin-2-ylmeth­yl)meth­oxy­aniline and mol­ecular bromine, the cyclo­hexa­none ring has a chair conformation with one of the four meth­oxy groups equatorially orientated with respect to the carbonyl group and the others axially orientated. The C—Br bond lengthsvary from 1.942 (4) to1.964 (4) Å. In the crystal, weak C—H⋯O_carbon­yl hydrogen-bonding inter­actions generate chains extending along the b-axis direction. Also present in the structure are two short inter­molecular Br⋯O_meth­oxy inter­actions [3.020 (3) and 3.073 (4) Å].

Chiral Polycyclic Ketones via Desymmetrization of Dihaloolefins

3-Chloronorbornenone (R)-1a (98% ee) was obtained from trichloronorbornene 5 in two steps by the in situ generation of dichloronorbornadiene 2a with t-BuOK and desymmetrization with (-)-ephedrine, followed by hydrolysis with PPTS. The generality of this desymmetrization with (-)-ephedrine was tested with dibromonorbornadiene 2c and other substituted dichloronorbornadienes.