William Dent

Diastereofacial selectivity in azomethine ylide cycloaddition reactions derived from chiral α-cyanoaminosilanes

Abstract A series of α-cyanoaminosilanes has been found to act as azomethine ylide equivalents. Treatment of these compounds with silver fluoride in the presence of electron deficient olefins gives substituted pyrrolidines in high yield. The extent ofdiastereoselectivity associated with the 1,3-dipolar cycloaddition of chiral azomethine ylides with several dipolarophiles has been studied. Reasonable levels of such diastereoselectivity have been found when optically active α-cyanoaminosilanes are employed as azomethine ylide equivalents. These compounds can be prepared in multigram quantities by treating the appropriate chiral amine with chlorotrimethylsilane followed by reaction of the resulting secondary amine with formaldehyde in the presence of potassium cyanide. It was found that N-benzyl-N-cyanomethyl-N-trimethylsilylmethylamine undergoes stereospecific cycloaddition with dimethyl fumarate and maleate. The stereospecificity of the reaction is consistent with a concerted cycloaddition reaction.

Cycloadditions of non-stabilized azomethine ylides and quinones synthesis of the Reniera isoindole

Abstract Azomethine ylides, generated from cyanomethylamino silanes and excess silver fluoride, undergo cycloaddition with quinones to give, after oxidation in situ , quinonoid isoindoles. This reaction provides the key step for a short, high yield synthesis of the Reniera isoindole 1a.

Bis-esters from maleic anhydrides under neutral conditions: Protection of the anhydride of the natural product cornexistin

Abstract Trimethylsilyldiazomethane converts maleic anhydride derivatives in alcoholic THF to bisesters. The highly acid and base sensitive natural product cornexistin was converted to its bis-methyl ester in 70–75% yield and to the mixed benzyl/methyl ester in 61% yield. The mixed ester can be converted back to cornexistin via transfer hydrogenation.