Carbonylation of Alkyl Radicals Derived from Organosilicates through Visible-Light Photoredox Catalysis.

Primary, secondary, and tertiary alkyl radicals formed by the photocatalyzed oxidation of organosilicates underwent efficient carbonylation with carbon monoxide (CO) to give a variety of unsymmetrical ketones. This study introduces the possibility of radical carbonylation under a photooxidative regime.

Rh-catalyzed [5+1] and [4+1] cycloaddition reactions of 1,4-enyne esters with CO: a shortcut to functionalized resorcinols and cyclopentenones.

We have developed novel Rh-catalyzed [n+1]-type cycloadditions of 1,4-enyne esters, which involve an acyloxy migration as a key step. The efficient preparation of functionalized resorcinols, including biaryl derivatives, from readily available 1,4-enyne esters and CO was achieved by Rh-catalyzed [5+1] cycloaddition accompanied by 1,2-acyloxy migration. When enyne esters had an internal alkyne moiety, the reaction proceeded by a [4+1]-type cycloaddition involving 1,3-acyloxy migration, leading to cyclopentenones.

Generation and trapping of cyclopentenylidene gold species: four pathways to polycyclic compounds.

Cyclopentenylidene gold complexes can easily be formed from vinyl allenes through a Nazarov-like mechanism. Such carbenes may transform in four different ways into polycyclic frameworks: electrophilic cyclopropanation, C-H insertion, C-C migration, or proton shift. We have studied the selectivity of these different pathways and used our findings for the expedient preparation of valuable complex molecules. An application to the total synthesis of a natural product, Delta(9(12))-capnellene, is presented. DFT computations were carried out to shed light on the mechanisms.

Generation of phosphorus-centered radicals via homolytic substitution at sulfur.

A novel radical domino process relying on the homolytic cleavage of P-S bonds allows the preparation of phosphorus-containing molecules through addition of P-centered radicals onto olefins. The key step of this reaction is a homolytic substitution on a sulfur atom. The scope of the reaction is broad. Diaminophosphonyl radicals whose reactivity was unknown react smoothly with olefins. Use of tin hydride can be avoided. A radical thiophosphinoylation of triple bonds has been uncovered. [reaction: see text]

Tandem gold(I)-catalyzed cyclization/electrophilic cyclopropanation of vinyl allenes.

We have developed an expedient method for the synthesis of polycyclic compounds from propargyl acetates or vinyl allenes involving up to three Au(I)-catalyzed elemental steps: 3,3-rearrangement, metalla-Nazarov reaction, and electrophilic cyclopropanation. The reaction proceeds under very mild conditions and in short times. The mechanism has been studied by DFT computations.

Preparation of fused polycyclic vinylcyclopropanes via radical cascade reactions.

Radical cascades employing (dichloromethyl)dimethylsilyl ethers as both a point of radical initiation and termination, allow efficient entry to fused polycyclic cyclopropanes, and are also suitable for the design of other radical processes terminated by beta-elimination of chloride.

Stereoselective transition metal-catalyzed and radical polycyclizations.

This short review presents a selection of metal-mediated and radical polycyclizations reported during the past two years. Palladium-catalyzed domino processes, cobalt-mediated cycloadditions and Pauson-Khand reactions catalyzed by rhodium are described. Ruthenium and platinum are shown as powerful metal catalysts in cyclizations, ring-closing metathesis and cycloisomerizations. Finally, recent examples of radical cascades, and their synthetic applications, are selected for their ability to build polycyclic compounds.

N-silyl-tethered radical cyclizations: a new synthesis of gamma-amino alcohols.

[reaction: see text] Various allylic and propargylic amines bearing a protecting group (PG) have been employed in N-silyl-tethered radical cyclizations. The resulting silapyrrolidine adducts could be smoothly oxidized, creating access to gamma-amino alcohols. The silylation, radical cyclization, and oxidation reactions could be consolidated in a one-pot process.

PtCl2-Catalyzed transannular cycloisomerization of 1,5-enynes: a new efficient regio- and stereocontrolled access to tricyclic derivatives.

[reaction: see text] Transannular PtCl(2)-catalyzed cycloisomerizations open a new route to cyclopropanic tricyclic systems. Ketones A or C were efficiently prepared from the same cycloundec-5-en-1-yne precursor B, depending on the substituent at the propargylic position (either benzoate or methoxy).

Synthesis of functionalized resorcinols by rhodium-catalyzed [5+1] cycloaddition reaction of 3-acyloxy-1,4-enynes with CO.

A novel [5+1] type carbonylative cycloaddition reaction has been developed using a Rh complex as catalyst. This reaction can convert readily available 3-acyloxy-1,4-enynes and CO to a wide range of functionalized resorcinols in good yields. A mechanism involving Rh-catalyzed cyclocarbonylation of 3-acyloxy-1,4-enynes accompanied by a 1,2-acyloxy shift is proposed for the present [5+1] type cycloaddition reaction.

PtCl2-catalyzed cycloisomerizations of 5-en-1-yn-3-ol systems.

5-En-1-yn-3-ol substrates bearing a free hydroxyl group or an acyl group are highly versatile partners for PtCl2-catalyzed cycloisomerizations. Electrophilic activation of the alkyne moiety triggers at wish a hydride or an O-acyl migration yielding at the end to regioisomeric keto derivatives. The efficient preparation of Sabina ketone, an important monoterpene precursor, has been worked out.