Oxabicyclo[3.2.1]octenes in organic synthesis--direct ring opening of oxabicyclo[3.2.1] systems employing silyl ketene acetals in concentrated solutions of lithium perchlorate-diethyl ether: application to the synthesis of the C(19)-C(27) fragment of rifamycin S.

[figure: see text] The direct opening at the bridgehead of oxabicyclo[3.2.1]octenes employing silyl ketene acetals in 4.0-5.0 M lithium perchlorate in diethyl ether has been realized, which gives rise to highly functionalized cycloheptadienes that can be further manipulated for use in natural product synthesis. The bridgehead opening reaction has been employed in the construction of the C(19)-C(27) fragment of Rifamycin S.

Baeyer-Villiger oxidation promoted by reaction of peracids with cyclic oxocarbenium ions generated in situ from internal hemiketals.

[reaction: see text] Reactive cyclic oxocarbenium ions, generated in situ from internal hemiketals, undergo Baeyer-Villiger oxidation upon exposure to m-chloroperbenzoic acid leading, after hydrolysis of the resultant lactones, to acyclic fragments for use in natural product synthesis.

Iodine(V) reagents in organic synthesis. Part 3. New routes to heterocyclic compounds via o-iodoxybenzoic acid-mediated cyclizations: generality, scope, and mechanism.

The discovery and development of the o-iodoxybenzoic acid (IBX) reaction with certain unsaturated N-aryl amides (anilides) to form heterocycles are described. The application of the method to the synthesis of delta-lactams, cyclic urethanes, hydroxy amines, and amino sugars among other important building blocks and intermediates is detailed. In addition to the generality and scope of this cyclization reaction, this article describes a number of mechanistic investigations suggesting a single electron transfer from the anilide functionality to IBX and implicating a radical-based mechanism for the reaction.