Versatile building blocks are key compounds in organic chemistry to construct complex molecules. In the course of our recent work, we discovered that α-amino allenylphosphonates (α-AAPs) are versatile products. They can be either oxidized to spirodienone lactams or reduced to α-amino vinylphosphonates (α-AVPs). Both structures are interesting from a synthetic point of view. Thus, we investigated the redox reactivity of α-AAPs, which are readily prepared from ynamido-alcohols. The partial reduction of the α-AAPs, conducted with a poisoned palladium catalyst under a hydrogen atmosphere, gave the α-AVPs and turns out to be stereoselective. The stereoselectivities Z/E go from 10/90 to 96/4. Furthermore we established some rules to predict the stereoselectivity, depending on the substitution on the allene moiety, on the phosphonate or on the nitrogen atom. We are now able to predict and control the stereoselectivity of the reduction. Moreover, in oxidative conditions (cerium(IV) ammonium nitrate), N-para-methoxybenzyl protected a-amino allenylphosphonates are transformed to spirodienone lactams in good to excellent yields. This 5-endo-dig cyclization proceeds through the formation of a key iminium intermediate. A comprehensive study on the nature of the solvent used for this reaction was undertaken resulting in the formation of three types of spirodienone scaffolds. We have proven the versatility of the α-AAPs and a comprehensive study on the redox properties of this compounds will be presented on this poster.

Redox behavior of α-amino allenylphosphonates: From α-amino vinylphosphonates to spirodienone lactams

251st National Meeting (2016)

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