Enantioselective Radical Cyclizations: A New Approach to Stereocontrol of Cascade Reactions

Abstract

Stereocontrol in a cascade radical addition-cyclization-trapping reaction was achieved by a new approach, which utilizes a hydroxamate ester moiety as a coordinating chiral Lewis acid tether between two radical acceptors. A remarkable feature of this reaction is the construction of three bonds and tertiary and quaternary stereogenic centers through both inter- and intramolecular carbon-carbon bond-forming processes. The chiral Lewis acid mediated reaction of oxime ethers also proceeded smoothly with good enantio- and diastereoselectivities, indicating the usefulness of the cascade approach for the asymmetric synthesis of various gamma-lactams.

Rhodium‐Catalyzed Enantioselective Radical Addition of CX4 Reagents to Olefins

“…More generally, asymmetric radical reactions of any type are rare, although notable successes have been achieved recently. [7] Most existing asymmetric radical reactions fall into one of three mechanistic classes. Most commonly, a radical adds to an olefin that is associated with a chiral metal complex ( 3 , Figure 2A).…”

Radicals in organic synthesis. Part 1

“…Many of these reagents will be discussed along with the appropriate transformations in the following sections. Interested readers are directed towards an excellent collection of reviews, which include diastereoselective radical reactions, 29a,b enantioselective radical reactions, [30][31][32] asymmetric additions to C]N bonds 12 and stereoselective conjugate additions. 33,34 An issue of Tetrahedron: Asymmetry was also dedicated to stereoselective radical reactions.…”

Regioselective Hydroxysulfenylation of α,β‐Unsaturated Imines: Enhanced Stability of an Intermediate Radical

“…[9] We considered that the stability of the intermediate radical would be increased by converting the carbonyl group of a,b-unsaturated aldehydes or ketones into the imino group, in particular under triethylborane-induced reaction conditions. [10] This concept is supported by the lower dissociation energy of the N À B bond than the O À B bond, which is related to the trapping process of the intermediate radicals A and B by the organoborane. [11] The ability of triethylborane to trap B was suppressed by the formation of PhSBEt 2 (4) as a result of rapid reaction with the thiol.…”