Alkenylidene in der organischen Synthese

Abstract

Uber Alkenylidene verlauft die selektive Bildung von Alkinen aus Aldehyden (oben links) und von Cyclopentenen aus Ketonen (oben rechts). Beide Reaktionen werden zunehmend in der Naturstoffsynthese genutzt, wie die Paare von Zwischenprodukten und Zielmolekulen unten belegen. OMe

Alkylidenecarbenes, Alkylidenecarbenoids, and Competing Species: Which Is Responsible for Vinylic Nucleophilic Substitution, [1 + 2] Cycloadditions, 1,5-CH Insertions, and the Fritsch−Buttenberg−Wiechell Rearrangement?

“…The computational thermodynamic picture agrees with observations 34 on rearrangements of alkynes in the gas phase, typically performed at ∼800 °C, which may be viewed as retro -1,2-shifts of hydrogen (R 2 ) in going from the alkynes R 1 C⋮CH ( 14 ) back to the alkylidenecarbenes R 1 CHC: ( 12 ). Despite the drastic thermal conditions, synthetically useful isomerizations were reported. ,, By coordination to certain transition metal ions − (M in R 1 CHCM) the carbene 12 (R 2 = H) can become more stable than the terminal alkyne R 1 C⋮CH from which it was created.…”

A Novel Synthetic Approach to Diaminoacetylenes: Structural Characterization and Reactivity of Aromatic and Aliphatic Ynediamines

“…[22] Mechanistically, the formation of 4 can be rationalized by an intramolecular insertion of the intermediate vinylidene species Int into an ortho-CÀH bond of one of the phenyl rings (Scheme 3), which resembles the formation of cyclopentene derivatives from thermally generated alkenylidenes by 1,5-CH insertion. [16,28] It should be noted, however, that insertion into alkyl C À H bonds is common, whereas examples of solution-state insertion into significantly less reactive aromatic CÀH bonds are rare and were only relatively recently reported.…”

Gold Vinylidene Complexes: Intermolecular C(sp3)H Insertions and Cyclopropanations Pathways

“…As cyclopropanation by gold carbenes is a frequently observed reactivity pattern, [5] we considered that goldvinylidene II might show comparable reactivity, and thus be a synthon for an alkylidene carbene. [6] An initial experiment with diyne substrate 4 a and a mixture of 5 mol % IPrAuNTf 2 and 10 mol % IPrAuPh or IPrAuMe (as an additive for acetylide formation)…”