Pd(II)-Catalyzed Conversion of Styrene Derivatives to Acetals:  Impact of (−)-Sparteine on Regioselectivity

Abstract

[reaction: see text] Pd[(-)-sparteine]Cl(2) catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride.

Katalytische selektive Synthese

“…[55] Wie Sigman et al berichteten, kann die Regioselektivität durch den Gebrauch von PdCl 2 ·Spartein umgekehrt werden. [56] Die Erklärung dieser Divergenz liegt in einem reversiblen Nucleopalladierungsschritt, in dem der ligandenfreie Pd-Katalysator den thermodynamischen Anti-Markownikoff-Weg beschreitet, der Spartein-Komplex jedoch das kinetische Markownikoff-Intermediat ergibt. Wacker-Oxidationen von terminalen Olefinen mit a-Heteroatom haben entweder schlechte oder unberechenbare Selektivitäten, was es schwierig macht, die immanente Präferenz eines bestimmten Alkens einzuschätzen.…”

Addition Reactions: Polar Addition

“…Initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd hydride. 73 Pd(II)-catalysed acetalization of terminal alkenes with electron-withdrawing groups CH 2 =CHX (X = CO 2 -alkyl, CN) has been reported to proceed smoothly in supercritical carbon dioxide under an oxygen atmosphere to produce (RO) 2 CHCH 2 X; polystyrene-supported benzoquinone (PS-BQ) or Cu II (Cu I ) chloride were employed as co-catalyst. The higher selectivity was achieved, without any chlorinated by-product detected, when using PS-BQ instead of the copper salts.…”

“…The regiochemistry of these cyclizations contrasts with the regiochemistry of intramolecular hydroaminations catalysed by lanthanide complexes, group III metal complexes, and platinum complexes, all of which have been reported previously to form cyclization products via Markovnikov addition. 101 Hydroformylation of 2-phenylsulfonyl-substituted norbornene (73) and norbornadiene derivatives, catalysed by the unmodified (acac)Rh(CO) 2 , has been reported to give, under standard conditions, exo-norbornane-and exo-norbornene-carboxaldehydes. The steric properties of the sulfonyl substituent, rather than its electronic effects, are believed to control the regioselectivity of the process.…”

A new approach to carbon–carbon bond formation: development of aerobic Pd-catalyzed reductive coupling reactions of organometallic reagents and styrenes

“…xiv Since the proposed mechanism of acetal formation involves initial nucleophilic addition of the alcohol to the metal bound alkene, we thought a less nucleophilic secondary alcohol, such as isopropanol (IPA), would not readily undergo acetal formation. However, performing the reaction with IPA as the solvent unexpectedly produced the hydroalkoxylation product 8 xv along with the Wacker oxidation product 7 , which most likely originates from an H 2 O 2 mediated pathway (Figure 3, B).…”