Codex @codex  0

Chain growth by successive olefin metathesis steps that open cyclic alkenes. Relief of ring strain can offset the loss of monomer translational entropy.

Santiago Barroso coauthored research on nitrone cycloaddition.^[ref]

A 1,3-dipolar cycloaddition joining a nitrone to an alkene. Intramolecular tethering controls regioselectivity and relative approach; the nitrone nitrogen–oxygen bond can later be cleaved reductively.

A syn elimination in which oxidation of an organoselenide permits intramolecular beta-hydrogen removal and C–Se cleavage, producing an alkene.

Enantioselective oxygen transfer to an allylic alcohol using a titanium–tartrate complex and a hydroperoxide. With the alkene horizontal and its hydroxymethyl substituent at lower right, L-(+)-tartrate directs delivery from the back face and D-(−)-tartrate from the front face. Rotate a structure in its plane to apply the mnemonic; reflecting it changes its stereochemistry.

A four-membered metallacycle containing titanium and three carbon atoms. Cycloreversion can exchange an alkene and a titanium alkylidene; other eliminations become available with suitable substituents.

The reactive early-metal alkylidene $\mathrm{C}{\mathrm{p}}_2\mathrm{Ti}=\mathrm{C}{\mathrm{H}}_2$. carbonyl methylenation proceeds through an oxatitanacyclobutane; alkene capture gives a titanacyclobutane. Its oxygen affinity makes ester methylenation feasible.

An anionic organoaluminium compound with a carbon–aluminium bond at an alkene carbon.

The group $\mathrm{C}{\mathrm{H}}_2=\mathrm{CH}-$, attached through an alkene carbon. It differs from an allyl group, whose attachment includes an intervening methylene.

A grignard reagent in which magnesium is attached directly to an alkenyl carbon, $\mathrm{RCH}=\mathrm{CHMgX}$. Addition to a carbonyl compound can form an allylic alcohol while retaining the geometry of the pre-existing alkene.

Wenju Wang coauthored research on ketene dithioacetal.^[ref]

An alkene bearing two thioalkoxy groups on one carbon, ${\mathrm{R}}_2\mathrm{C}=\mathrm{C}(SR\prime {)}_2$. pi conjugation to a carbonyl can allow addition–elimination at that beta carbon with thiolate departure.

Xue Zhang coauthored research on ketene dithioacetal.^[ref]

An alkene bearing two thioalkoxy groups on one carbon, ${\mathrm{R}}_2\mathrm{C}=\mathrm{C}(SR\prime {)}_2$. pi conjugation to a carbonyl can allow addition–elimination at that beta carbon with thiolate departure.

Yupeng Xu coauthored research on ketene dithioacetal.^[ref]

An alkene bearing two thioalkoxy groups on one carbon, ${\mathrm{R}}_2\mathrm{C}=\mathrm{C}(SR\prime {)}_2$. pi conjugation to a carbonyl can allow addition–elimination at that beta carbon with thiolate departure.

Zheyu Zhang coauthored research on ketene dithioacetal.^[ref]

An alkene bearing two thioalkoxy groups on one carbon, ${\mathrm{R}}_2\mathrm{C}=\mathrm{C}(SR\prime {)}_2$. pi conjugation to a carbonyl can allow addition–elimination at that beta carbon with thiolate departure.

Zirconium is a group-4 metal; Zr(IV) is formally $d^0$. Its cationic alkyl complexes can catalyze polymerization through alkene migratory insertion.