Ruthenium‐catalyzed cyclizations of enynes via a ruthenacyclopentene intermediate: Development of three novel cyclizations controlled by a substituent on alkyne of enyne

Abstract

Three novel ruthenium-catalyzed cyclizations of enynes were developed. In each cyclization, a ruthenacyclopentene derived from enyne and Cp*RuCl(cod) is a common intermediate. When an enyne having an alkyl, an ester, or a formyl group on an alkyne was reacted with Cp*RuCl(cod) under ethylene gas, ethylene was inserted into the ruthenium-sp(2) carbon bond of ruthenacyclopentene to afford ruthenacycloheptene, and β-hydrogen elimination followed by reductive elimination occurred to give a cyclic compound having a 1,3-diene moiety. When an acyl group was placed on the alkyne, the carbonyl oxygen coordinated to the ruthenium metal of ruthenacyclopentene to produce a ruthenium carbene complex, which reacted with ethylene to give a cyclic compound having a cyclopropane ring on the substituent. On the other hand, when the substituent on the alkyne was pent-4-enyl, insertion of an alkene part into ruthenacyclopentene followed by reductive elimination gave a tricyclic compound by a ruthenium-catalyzed [2+2+2] cyclization of diene and an alkyne.

Transition‐Metal‐Catalyzed Laboratory‐Scale Carbon–Carbon Bond‐Forming Reactions of Ethylene

“…[64] For example, in 1998, Mori and co-workers observed a dramatic reactivity difference in the intramolecular ring-closing enyne metathesis (RCEYM) of terminal-alkyne-bearing substrates such as 90 in the presence of ethylene (Scheme 24). [65] They noted a low yield of 91 under an argon atmosphere, but under an atmosphere of ethylene quantitative yield was observed in just 2.5 hours.…”

Übergangsmetallkatalysierte C‐C‐Kupplungen mit Ethylen im Labormaßstab

“…[64] Beispielsweise berichteten Mori und Mitarbeiter 1998 über eine drastische Reaktivitätssteigerung bei der intramolekularen RingschlussEnin-Metathese (RCEYM) von terminalen Alkinen wie 90 in Gegenwart von Ethylen (Schema 24). [65] [71] Ruthenium(II)-katalysierte Alkinfunktionalisierungen, die einen oxidativen Ruthenacyclopentenierungsschritt durchlaufen, erçffnen wie oben gezeigt einen selektiven Zugang zu interessanten und potentiell nützlichen Produkten.…”

“…Es liegen zahlreiche Verçffentlichungen über inter-und intramolekulare Enin-Metathesen vor, die durch die Gegenwart von Ethylen beschleunigt werden. [64] Beispielsweise berichteten Mori und Mitarbeiter 1998 über eine drastische Reaktivitätssteigerung bei der intramolekularen Ringschluss-Enin-Metathese (RCEYM) von terminalen Alkinen wie 90 in Gegenwart von Ethylen (Schema 24). [65] Für das Produkt 91 wurde unter Argon nur eine geringe Ausbeute gefunden, während unter einer Ethylenatmosphäre eine quantitative Ausbeute nach nur 2.5 h beobachtet wurde.…”

Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

“…In particular, cycloisomerization of enynes allows one to prepare compounds with exocyclic double bonds and cyclopropanes in a highly selective manner [5–7]. While catalytic transformations of enynes have been investigated in detail, there are only a few examples of similar reactions of dienynes [8–14]. Among dienynes, 1,11-dien-6-ynes 1 are of particular interest, because they are readily available in 1–2 steps from the commercial precursors (e.g., allyl bromides and 1,4-dibromo-2-butyne).…”