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Stereoselective Aminoxylation of Biradical Titanium Enolates with TEMPO
Author(s) -
GómezPalomino Alejandro,
Pellicena Miquel,
Romo Juan Manuel,
Solà Ricard,
Romea Pedro,
Urpí Fèlix,
FontBardia Mercè
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201402127
Subject(s) - moiety , diastereomer , chemistry , adduct , regioselectivity , stereoselectivity , titanium , alkyl , aryl , medicinal chemistry , organic chemistry , catalysis
A highly efficient and straightforward aminoxylation of titanium(IV) enolates from ( S )‐ N ‐acyl‐4‐benzyl‐5,5‐dimethyl‐1,3‐oxazolidin‐2‐ones with TEMPO has been developed. A wide array of functional groups on the acyl moiety, including alkyl and aryl substituents, olefins, esters, or α‐cyclopropyl, as well as α‐trifluoromethyl groups, are well tolerated. This transformation can therefore produce the α‐aminoxylated adducts in excellent yields with high diastereomeric ratios (d.r.). In turn, parallel additions to the α,β‐unsaturated N ‐acyl counterparts give the corresponding γ‐adducts with complete regioselectivity in moderate to good yields. Removal of the piperidinyl moiety or the chiral auxiliary converts the resultant adducts into enantiomerically pure α‐hydroxy carboxyl derivatives, alcohols, or esters in high yields under mild conditions. Finally, a new mechanistic model based on the biradical character of the titanium(IV) enolates has been proposed.