Current Organic Synthesis - Volume 4, Issue 3, 2007

The present review is mainly focused upon the use of C-substituted oxazolidin-2-ones as chiral auxiliaries in the stereocontrolled C-C and C-X (X = hetero atom) bond formation. The recent progress in the stereoselective alkylation, cycloaddition and aldol reaction, as well as in the 1,4-coniugate addition, in [2+2]- photocycloaddition, in Lewis acid promoted free-radical copolymerization reactions are discussed. Emerging new applications of the oxazolidin- 2-one nucleus, such as building blocks in the design and preparation of foldamers or as organocatalyst in enantioselective epoxidation reactions, will be also discussed.

Organic carbamates classically have been synthesized using harmful reagents like phosgene, its derivatives and carbon monoxide. Recently, carbon dioxide has been used as a cheap and harmless reagent as an alternative to harmful reagents for the synthesis of organic carbamates in gaseous, supercritical and electrochemical forms. The present review will deal the synthesis of organic carbamates from various starting materials from beginning to recent ones.

Free radical reactions have become increasingly important, as well as a very attractive tool, in organic synthesis within the last two decades, due to their powerful, selective, specific, and mild reaction abilities. Mn(OAc)3 mediated oxidative free radical reactions have been extensively developed in the last twenty years. Numerous regio-, chemo-, and stereoselective synthetic methods have been developed in both inter- and intramolecular reactions, and have detailed the progress of Mn(OAc)3 mediated oxidative free radical reactions since the end of the 19th century. The new literature about the new synthetic methods on Mn(OAc)3 mediated carbon-carbon bond formation and carbon-oxygen bond formation reactions has not been extensively reviewed. The present paper summarizes the recent developments in oxidative free radical reactions mediated by Mn(OAc)3. Mn(OAc)3 mediated reactions of conjugated systems (e.g., alkenes, alkynes, 1,3-alkadienes, l,3-alkadiynes, 1-alken-3-ynes) with β-dicarbonyl compounds, Mn(OAc)3 mediated alkylation, such as the oxidative addition of an aldehyde or ketone to alkenes, Mn(OAc)3 mediated free-radical cyclization of alkenes with active methylene compounds in the presence of oxygen to afford the cyclic peroxides; lactone synthesis by the Mn(OAc)3 mediated oxidative addition of carboxylic acids to alkenes, Mn(OAc)3 mediated cyclization of α- (methylthio)acetamides, enamides, and β-keto carboxamides to afford cyclic products. Mn(OAc)3 oxidative free-radical cyclizations of allylic β-dicarbonyl compounds, for example, the cyclization of allylic β-ketoesters to afford the corresponding γ-lactone. The reaction of alkenes with sodium azide in the presence of acetic acid was investigated to afford 1.2-diazides. The selective oxidation of enones led to α'-acetoxy-enones by Mn(OAc)3 oxidation. In general, Mn(OAc)3 oxidations are characterized by higher α'-regioselectivity and chemical yields, and milder reaction conditions, in turn tolerating many sensitive functional groups. The use of Mn(OAc)3 in combination with other carboxylic acids or manganese(II) carboxylates extends this methodology to the preparation of a variety of α'-acyloxyenones that are otherwise inaccessible in a one-step procedure.