Investigation of UV Light-Promoted Synthesis of α-Sulfonyl Amides from N-Sulfonyl Ynamides.

UV light-promoted synthesis of α-sulfonyl amides from N-sulfonyl ynamides without any additives is reported. The reaction proceeds through a radical chain mechanism involving the photoinduced cleavage of the nitrogen-sulfur bond and addition of an electrophilic sulfonyl radical to the triple bond of the ynamide followed by ß-fragmentation of the sulfonyl group leading to a ketenimine hydrated upon workup. This highly efficient rearrangement leads, after acidic treatment, to a wide range of α-sulfonyl amides in high yields.

Ynamides in Radical Reactions: A Route to Original Persubstituted 2-Aminofurans.

Mn(OAc)3/Cu(OAc)2-mediated reaction between ynamides, derived from oxazolidone or 3-methylindole carboxylate, and cyclic α-dicarbonyl radicals led to the one-pot synthesis of 2-aminofurans. The transformation involves addition of the α-dicarbonyl radical to ynamide, oxidation to ketene-iminium, and polar cyclization steps to provide original persubstituted 2-aminofurans in good to excellent yields. This work represents the first radical route for the synthesis of furans from ynamides.

Intermolecular Addition of Carbon-Centered Radicals to Ynamides. A Regio- and Stereoselective Route to Persubstituted α-Iodo-enamides.

Rather surprisingly, C-C bond formation through "intermolecular" radical addition to internal ynamides has never been reported. Actually, ynamides are excellent acceptors for "electrophilic" carbon-centered radicals. These processes enable the introduction of functionalized alkyl chains at Cß, groups that have not yet been introduced via the addition of organometallics. Radical carboiodination affords persubstituted α-iodo-enamides in moderate to high yield. The addition is totally stereoselective. Theoretical support to the mechanism and the scope and limitation of the reaction are discussed.

Chiral Fidelity in the Diastereoselective and Enantiospecific Synthesis of Indenes from Axially Chiral Benzylidene Cyclanes.

Enantioenriched indenes were reached through a chirality conversion strategy using original axially chiral benzylidene cyclanes. Good to high remote diastereocontrol and excellent enantiocontrol were observed in this cascade involving copper-catalyzed homologation of terminal alkynes, in situ allenoate formation and Alder-ene cyclization.

Double transfer of chirality in organocopper-mediated bis(alkylating) cycloisomerization of enediynes.

An original synthesis of chiral benzofulvenes triggered by organocopper reagents is reported. These enantiopure products are available through a highly chemo-, regio-, diastereo-, and enantioselective bis(alkylating) cycloisomerization process. A double chirality transfer (central-to-axial-to-central) is observed.

Theoretical support for the involvement of a radical pathway in the formation of allenylzincs from propargyl iodides and dialkylzincs: influence of zinc coordination.

Propargyl iodides are good precursors for allenylzincs via reaction with diethylzinc, even in nondegassed medium. These reactions proceed via zinc/iodine exchange. Owing to the previously reported detection of propargyl radical by ESR experiments, in this process a radical mechanism was suspected. Calculations of the C-Zn BDEs in allenyl- and propargylzinc species were performed with the CBS-QB3 method to demonstrate that propargyl radicals could undergo homolytic substitution at zinc. The stabilization of allenylzinc derivatives by chelation, made possible by the selection of appropriate ortho-substituted 3-phenylalkynyl iodides as precursors, was shown to influence the regioselectivity of their addition to aldehydes and ketones. The more stabilized the chelated allenylzinc intermediate, the higher the ratio of homopropargylic alcohols.

Aminomethylation of Michael acceptors: complementary radical and polar approaches mediated by dialkylzincs.

Phtalimidomethyl iodide and substituted maleimidomethyl iodide were used as radical precursors in dialkylzinc-mediated radical addition to diethyl fumarate. The reactions led stereoselectively to functionalized pyrrolizidines. The radical mechanism was supported by spin-trapping experiments and rationalized by theoretical calculations. Radical additions, on the one hand, and carbozincation followed by transmetalation with copper(I), on the other, were shown to be complementary methods to achieve the formal aminomethylation of activated unsaturated compounds.