Lactone synthesis by electron transfer and radical chemistry

Abstract

Abstract

Hydrogen-Bonding as a Stereocontrolling Element in Free-Radical C-Allylation Reactions: Vicinal, Proximal, and Remote Asymmetric Induction in the Amino Acid Series

“…Continuing our studies on the reactivity and stereochemical issues related to α-carbalkoxy radicals, we report herein examples of remarkably high stereoselectivity in 1,2-induction 2,3 and unprecedented 1,3-, 1,4-, and 1,5-asymmetric inductions in the free-radical C -allylation of α-acyl radicals derived from a series of N -substituted acyclic amino acid derivatives (Scheme 1), by exploiting intramolecular H-bonding as a stereocontrolling element.

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Triethylborane-Mediated Atom Transfer Radical Cyclization Reaction in Water

“…We speculate that water can effectively decrease the barrier to rotation between the major Z -rotamer and minor E -rotamer which can cyclize (Scheme ) . Curran and Tamine have suggested that Z and E conformers of the radical are not sufficiently interconverting in benzene at 25 °C 6h. In water, however, the interconversion of the rotamers might occur as a result of the decrease of the barrier and cyclization from E -rotamer could afford lactone 2 .…”

“…We chose an atom-transfer cyclization of allyl iodoacetate as a model reaction in water. The indirect bromoacetal method was developed by Stork and Ueno because direct cyclization of α-halo esters into γ-butyrolactones is a relatively slow radical reaction . Lactones are usually produced from this strategy by oxidation of the products prepared from radical cyclization of bromoacetal.…”

Hexenyl radical cyclization via phenyl selenide transfer

“…It is also important to note that radical cyclizations of unconstrained esters such as 5 and 7 are quite rare, owing to the large barrier to rotation about the CO-0 bond which inhibits the formation of the proper conformer for cyclization. 8 The cyclization of the ketoester 8 (Scheme l), yielded a more complex product mixture. Photolysis of 8 generated a 60% yield of the cyclohexanone 12 and a 20% yield of the cyclopentanone 13 (ring methine coupling of 6 Hz).…”