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Starting from a historical background that acknowledges isonitriles as a neglected class of compounds due to their unpleasant smell and hardly controlled reaction conditions with open shell species, the present concept article aims at highlighting the seeds of the modern isonitrile photochemistry. Representative essential transformations achieved via either UV light irradiation or radical initiators at high temperatures are brought into play to draw a parallel with the current literature relying on the exploitation of visible light photochemical methods. Such a comparison points out the potential of this enabling technology to further expand the scope of isonitrile chemistry and the unmet challenges which makes it a very stimulating field. [ABSTRACT FROM AUTHOR]

Nucleosides with a substituent at the 4'-position have received much attention as antiviral drugs and as raw materials for oligonucleotide therapeutics. 4'-Modified nucleosides are generally synthesized using ionic reactions through the introduction of electrophilic or nucleophilic substituents at the 4'-position. However, their synthetic methods have some drawbacks; e.g., (i) it is difficult to control stereoselectivity at the 4'-position; (ii) complex protection-deprotection processes are required; (iii) the range of electrophiles and nucleophiles is limited. With this background, we considered that a carbon radical generated at the 4'-position would be a useful intermediate for the synthesis of 4'-modified nucleosides. In this review, two novel methods for the generation of 4'-carbon radicals are summarized. The first utilizes radical deformylation involving β-fragmentation of a hydroxymethyl group at the 4'-position. The other utilizes radical decarboxylation and 1,5-hydrogen atom transfer (1,5-HAT), which enables the generation of 4'-carbon radicals while retaining the hydroxymethyl group at the 4'-position. These methods enable the rapid and facile generation of 4'-carbon radicals and provide various 4'-modified nucleosides including 2',4'-bridged structures.

The three-component free-radical carbo-alkenylation of electron-rich olefins has been studied, varying the substitution pattern in the alkene, in the radical precursor and in the final acceptor. New vinylsulfones were also prepared and their reactivity investigated. The scope and limitations of the process was established, and the reaction mechanism clarified using selected dienes as radical clocks. It was thus recognised that the reversible addition onto the olefin of the released sulfonyl group is an important event, which should not be overlooked when using such multicomponent carbo-alkenylation reactions. [ABSTRACT FROM AUTHOR]

This review provides an overview of the recent progress made in the area of free-radical additions across the ?-system of olefins, with a focus on the role of sulfonyl derivatives as one of the reaction partners in multicomponent processes. The mechanism and utility in organic synthesis of carbo-alkenylation, alkynylation, oximation and azidation of olefins are thus discussed and illustrated with some applications in total synthesis of natural products.

5-hydroxy-1-oxo-5α-cholestan-3β-yl acetate (11) was prepared in 5 steps starting from (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one (6). Treatment of the 1-oxo-5-hydroxy derivative 11 with lead tetraacetate (LTA) (under thermal or hypoiodite conditions) or with mercuric oxide/iodine (HgO/I2) reagent resulted in the oxidative β-fragmentation of the C(5)–C(10) bond affording 1,5-dioxo-5,10-secocholest-10(19)-en-3β-yl acetate (12), in different yields, depending on the reagent. Also the stereochemistry of the 1β,6β-cyclization product 13, formed by transannular cyclization of the 1,5-diketone 12 on silica gel, is discussed in this work.

Abstract: The reaction of derivatives on C3 of 6-hydroxy-2,7-dimethyl-11-oxatricyclo[6.2.1.02,6]undecan-4-one with lead tetraacetate and iodine, gave, in a good yield, 1,7-epoxycyclononanes. These compounds are the result of a β-fragmentation at the level of C2–C6 respect to the tertiary hydroxyl group on C6, with an unexpected contraction from a ten to a nine-membered ring system, via a radical addition to the carbonyl group on C4. The treatment of precursors (non-functionalized on C3) with LTA and iodine produced again a β-fragmentation without any structural rearrangement, affording a typical 1,8-epoxycyclodecane system. The transformation of the carbonyl group on C4 into acetate avoided radical additions and rearrangements affording, in high yield, the corresponding cyclodecanes. By this methodology, either 1,7-epoxy-cyclononane or 1,8-epoxycyclodecane could be synthesized, in a good yield, from the same versatile precursor. [Copyright &y& Elsevier]