Roberto Ignacio

Reactions of Conjugate Phosphinyl- and Phosphonyl-Nitroso Alkenes with Enamines. Preparation of N-Hydroxypyrrole Derivatives†

The synthesis of highly functionalized N-hydroxypyrrole derivatives by the formal [3+2] cycloaddition reaction of enamines and nitroso alkenes derived from phosphine oxides and phosphonates is reported. Intermediate phosphorylated nitrones, whose formation can be explained by a conjugate addition of enamines to phosphorylated nitroso alkenes and formation of the five-membered heterocycles, are isolated.

Hetero-Diels-Alder reaction of phosphorylated nitroso alkenes with enol ethers on water: a clean approach toward 1,2-oxazine derivatives.

A concise and eco-friendly synthesis of highly functionalized 1,2-oxazines from phosphinyl- and phosphonyl-nitroso alkenes has been developed. The key step of this process, which involves a two-step sequence of reactions on-water, is a regioselective hetero-Diels-Alder cycloaddition reaction of enol ethers to 4-phosphinyl or 4-phosphonyl nitroso alkenes mediated by water itself. The process has also been performed under solvent-free conditions and in organic solvents for comparison.

Hetero-Diels-Alder reaction of phosphinyl and phosphonyl nitroso alkenes with conjugated dienes: an aza-Cope rearrangement.

Phosphorylated nitroso alkenes react with cyclic dienes such as cyclopentadiene or cyclohexadiene to afford hetero Diels-Alder-type cycloadducts where the nitroso alkene participates as dienophile component and the cyclic olefin acts as the 4π-electron (diene) system. Subsequent aza-Cope rearrangement affords highly functionalized 5,6-dihydro-4H-1,2-oxazines. Conversely, the reaction of TMS-substituted cyclopentadiene (dienophile) with nitroso alkenes as heterodienes leads directly to bicyclic 1,2-oxazines. Theoretical studies are in agreement with the experimental results and with the new aza-Cope rearrangement proposed.

Phosphorated 1,2-Oxazabuta-1,3-dienes as Synthetic Tools for the Preparation of α-Amino Phosphorus Derivatives and Functionalized Nitrogen-Containing Heterocycles

Abstract An efficient method for the synthesis of phosphorated 1,2-oxazabuta-1,3-dienes derived from phosphine oxides and phosphonates has been developed by means of base-mediated dehydrohalogenation of readily available α-halooximes. New functionalized α-amino phosphorus derivatives are easily available, in a regioselective way, through conjugate addition of amino nucleophilic reagents such as ammonia, primary or secondary amines, and optically active amino esters to these highly reactive nitroso derivative Michael acceptors. Phosphorated 1,2-oxazabuta-1,3-dienes also react with enamines in a formal [3 + 2] cycloaddition to afford highly functionalized phosphorated N-hydroxypyrrole derivatives.