Practical radical cyclisations leading to the construction of near-stereopure quaternary carbon stereogenic centres

Abstract

The 2,3,4,6-tetra-O-acetyl-b-D-glucopyranosyl auxiliary is effective in directing bromopropargyloxy additions to the olefinic bonds of vinylogous esters/carbonates; in the presence of AIBN and 1-ethylpiperidinium hypophosphite, the adducts undergo highly stereoselective reductive radical cyclisations in which quaternary carbon stereogenic centres are generated.

A Computational Study of Radical Haloacetal Cyclizations Controlled by the Acetal Center

“…[20] A related example with complete stereocontrol has been reported by Stoodley. [19] The corresponding ester and cyano substituted radical 3 c and 3 d were also investigated (Table 4, entries 3 and 4); in both cases, complete stereoselectivity in favor of the 2,3-trans-4,5-trans compound is predicted; this confirms the directional importance of electron withdrawing substituents in these reactions. No experimental data are available for comparison with these substrates.…”

Electroreductive Radical Cyclization of Ethyl 2‐Bromo‐3‐allyloxy‐ and‐3‐(propargyloxy)propanoates Catalyzed by (Tetramethylcyclam)nickel(I) Electrogenerated at Carbon Cathodes in Dimethylformamide

“…In addition, 1-ethylpiperidinium hypophosphite and hypophosphorous acid can serve as effective reducing agents for organic halides. [8,9] For processes involving radicals, a recent advance has been the introduction of solid-phase organic synthesis, [10][11][12] for which the radical precursor is attached to a resin and the Bu 3 SnH used in the reaction is removed by simple washing of the resin after the intramolecular cyclization is complete; thus, the desired product can be obtained easily and in a highly pure state.…”

Diastereoselective Radical‐Mediated Hydrogen‐Atom Abstraction

“…For instance, by using acetals of type 1 and 3, it is possible to activate alcohols at the b position. The chromatographic resolution of the starting acetals and the use of a chiral auxiliary to control the absolute stereochemistry at the acetal chiral center [11,13,[21][22][23] should facilitate access to optically pure polysubstituted tetrahydrofurans and g-lactones. Further work toward this goal is currently underway.…”