Zirconium mediated synthesis. Convergent access to terminal trienes, dienes, and dienynes

Shelf-Stable (E)- and (Z)-Vinyl-λ3-chlorane: A Stereospecific Hyper-vinylating Agent

We report the first stereoselective synthesis of stable (E)- and (Z)-β-chlorovinyl-λ³-chlorane via direct mesitylation of 1,2-dichloroethylene with mesityldiazonium tetrakis(pentafluorophenyl)borate under mild reaction conditions. The structure of the (E)-vinyl-λ³-chlorane was established by single-crystal X-ray analysis. Because of the enormously high leaving group ability of the aryl-λ³-chloranyl group, vinyl-λ³-chloranes undergo not only S_NVσ-type reaction with extremely weak nucleophiles such as perfluoroalkanesulfonate, iodobenzene, and aromatic hydrocarbons but also coupling with phenylcopper(I) species.

Homologation chemistry with nucleophilic α-substituted organometallic reagents: chemocontrol, new concepts and (solved) challenges

The transfer of a reactive nucleophilic CH2X unit into a preformed bond enables the introduction of a fragment featuring the exact and desired degree of functionalization through a single synthetic operation. The instability of metallated α-organometallic species often poses serious questions regarding the practicability of using this conceptually intuitive and simple approach for forming C-C or C-heteroatom bonds. A deep understanding of processes regulating the formation of these nucleophiles is a precious source of inspiration not only for successfully applying theoretically feasible transformations (i.e. determining how to employ a given reagent), but also for designing new reactions which ultimately lead to the introduction of molecular complexity via short experimental sequences.

Stereoselective generation of (E)- and (Z)-2-fluoroalkylidene-type carbenoids from (2-fluoro-1-alkenyl)iodonium salts and their application for stereoselective synthesis of fluoroalkenes

Alkylidene-type carbenoids, generated from (Z)- or (E)-(2-fluoro-1-alkenyl)iodonium salts by treatment with LDA, reacted with trialkylboranes to give (E)- or (Z)-(fluoroalkenyl)boranes stereoselectively. The resulting (fluoroalkenyl)borane can be used for the selective synthesis of (E)- or (Z)-fluoroalkenes, (E)- or (Z)-fluoroiodoalkenes, and alpha-fluoroketones. [reaction: see text]

Stereoselective preparation of dienyl zirconocene complexes via a tandem allylic C-H bond activation-elimination sequence

Several dienyl zirconocene derivatives were easily prepared, as unique geometrical isomers, from simple non-conjugated unsaturated enol ethers with (1-butene)ZrCp2 complexes. This new methodology is based on a tandem allylic C-H bond activation-elimination sequence and the mechanism has been mapped out by deuterium labeling experiments. The stereochemical outcome of this process was determined by addition of several electrophiles. Moreover, when the organometallic derivative is vinylic as well as allylic such as in 44-47Zr, an unexpected reversal of the stereochemistry has been found during the zirconium to copper transmetalation step.

New approach to the stereoselective synthesis of metalated dienes via an isomerization-elimination sequence

Treatment of Cp2ZrBu2 with enol ether containing a remote double bond lead to conjugated metalated diene as single isomer via a tandem isomerization-elimination sequence. 2-Arylsulfonyl 1,3-dienes can also be used as a source of dienyl zirconocene derivatives, and the stereochemistry of the diene is dependent on the transmetalation reaction.