A Zirconium Promenade - An Efficient Tool in Organic Synthesis

Abstract

The one-pot preparation of allyl-and dienyl-zirconocene derivatives can be easily achieved via a tandem allylic C-H-activation-b-elimination reaction from unsaturated fatty alcohol and enol ether derivatives, respectively. The reaction proceeds rapidly, under mild conditions, and is insensitive to the length of the carbon tether between the double bond and the leaving group moiety.

Remote functionalization of hydrocarbons with reversibility enhanced stereocontrol

“… 10 It should be noted that under the same experimental conditions, saturated cyclopropane (not possessing the remote double bond) does not lead to the carbon–carbon bond cleavage of the three-membered ring, confirming our hypothesis that the initiating step on the alkenyl moiety is required for the reaction to proceed. The allylic C–H bond activation most probably proceeds through the formation of an η 3 -allyl intermediate 7 , 8 and the unique selectivity of the ring-opening results from the kinetically and thermodynamically preferred formation of primary organometallic species 2 over tertiary organometallic species in the ring cleavage (C 1 –C 2 cleavage preferred over C 1 –C 3 , Scheme 3 ). 11 Moreover, the reactivity of the bismetalated species (also called metallacycle) 2 can be fully controlled as the reactivity of the allylzirconocene moiety (C 1 –Zr) is higher than the reactivity of the alkylzirconocene (C 2 –Zr) moieties towards electrophiles.…”

“…However, due to the natural propensity for statistical isomerization, the selective migration of a metal complex along a hydrocarbon chain can only be directed if associated with a strongly thermodynamically favoured termination step. In this context, we have reported the transformation of unsaturated fatty alcohol derivatives as a source of substituted allylmetal species (Path A, Scheme 1 ) 7 and the stereoselective preparation of conjugated dienyl metal complexes from non-conjugated enol ethers (Path B, Scheme 1 ) 8 where the irreversible termination step is an elimination reaction. Initiating reversible allylic C–H bond activations triggered these reactions and up to 6 carbon atoms separated the initial double bond from the terminating center.…”

Einfacher Zugang zu modifizierbarem Schwartz‐Reagens – Oxidative Addition von amidischen N‐H‐Bindungen an reduzierte Zirconocenkomplexe

“…Hydrozirconierungen spielen in der Synthesechemie eine essenzielle Rolle, da sie die direkte Funktionalisierung von unreaktiven Olefinen ermöglichen 1b,c. Die Verwendung von terminalen Alkenen führt zu sterisch nahezu ungehinderten primären Zirconocen‐Alkylkomplexen 27. Diese linearen Reaktionsprodukte können ebenfalls durch die Umsetzung interner Alkene erhalten werden.…”

“…Diese linearen Reaktionsprodukte können ebenfalls durch die Umsetzung interner Alkene erhalten werden. Die Reaktion läuft dabei über eine β‐Hydrideliminierung sowie eine Re‐Insertion, aus der die Wanderung der [Cp 2 Zr]‐Einheit zur terminalen Position resultiert 27. Die Verwendung von Arylalkenen führt zu einer Störung der Regioselektivität, sodass sowohl lineare als auch verzweigte Produkte entstehen 28…”

Cyclopropenylcarbinol Derivatives as New Versatile Intermediates in Organic Synthesis: Application to the Formation of Enantiomerically Pure Alkylidenecyclopropane Derivatives

“…[46] The same trend was observed when the intermediate cyclopropylaluminum species possessing alkyl groups R 3 was heated either at 80 8C in benzene (or stirred for a longer period of time in Et 2 O at reflux). [46,47] Preparation of enantiomerically enriched alkylidenecyclopropane derivatives: By following the strategy that we described in Scheme 5 for the preparation of racemic alkylidenecyclopropanes from cyclopropenylcarbinols, enantiomerically pure alcohols 2 were treated with various Grignard reagents in the presence of 20 mol % of CuI as described in Scheme 12.…”