Ruthenium-Catalyzed Enyne Cycloisomerizations. Effect of Allylic Silyl Ether on Regioselectivity

Abstract

The ruthenium-catalyzed cycloisomerization of 1,6- and 1,7-enynes substituted in the terminal allylic position with a tert-butyldimethylsilyl ether group emerges as an effective reaction to form unprecedented five- or six-membered rings possessing a geometrically defined enol silane. Straightforward synthetic access to a variety of achiral 1,6- and 1,7-enynes, as well as chiral ones, is presented. Ruthenium catalysts effect efficiently such single-step cycloisomerization at room temperature in acetone under neutral conditions. The cycloisomerization functions with (E) or (Z) 1,2-disubstituted alkenes. Parameters influencing the enol silane geometry are discussed. The level of selectivity depends on the alkyne substitution, the geometry of the double bond, and the nature of the catalyst. Furthermore, examples of stereoinduction are shown and lead to highly substituted carbo- and heterocycles with excellent diastereocontrol.

Exploiting the Pd- and Ru-Catalyzed Cycloisomerizations: Enantioselective Total Synthesis of (+)-Allocyathin B2

“…Alkyne 11 was synthesized in satisfactory yield through the addition of lithium dimethylcuprate to 8 followed by treatment of the resulting ketone 9 with LDA and PhNTf 2 36 followed by a Sonogashira coupling reaction (Scheme 2). 2 44 are ineffective catalysts in the cycloisomerization of 14.…”

“…2 44 are ineffective catalysts in the cycloisomerization of 14. Prior efforts in our laboratory indicate that palladium systems are more tolerant of olefin substitution than ruthenium in these reactions.…”

“…In 1979, Ayer et al reported the isolation and structure of (+)-allocyathin B 2 (1, Scheme 1), 5 a member of the cyathin terpenoids. 5-13 Compound 1, a metabolite from the fruit bodies of Cyathus earlei Lloyd, is distinguished by an angularly fused 5-6-7 tricyclic skeleton with a highly unsaturated trienal motif embedded in the framework and 1,4-anti quaternary methyl groups located at the ring junctions.…”

“…A preliminary report describing only the total synthesis has recently appeared. 31 Herein we report an enantioselective total synthesis of (+)-allocyathin B 2 . The goal of this synthesis was to develop a catalytic approach to enantioselectively install the first quaternary carbon and relay the stereochemical information to the remaining two stereogenic centers.…”

Ruthenium‐katalysierte Reaktionen – eine Schatzkiste für atomökonomische Umwandlungen

“…[192] (60)]. [193] Bei unsymmetrischen, trisubstituierten Olefinen gibt es zwei Möglichkeiten, ein b-Hydridion zu abstrahieren, wobei zwei unterschiedliche Produkte entstehen. Es wird jedoch, abhängig von der ursprünglichen Olefinkonfiguration, jeweils ein Reaktionsweg stark bevorzugt.…”