2,2‐Dimethyl‐α,α,α′,α′‐tetra(naphth‐2‐yl)‐1,3‐dioxolan‐4,5‐dimethanol (DINOL) für die Titanat‐vermittelte, enantioselektive Addition von Diethylzink an Aldehyde

Abstract

Auch an aliphatische Aldehyde wird in bisher kaum erreichten Selektivitäten (bis > 99.5:0.5) Et2Zn enantioselektiv addiert, wenn als Katalysator das Siebenringtitanat 1 und stöchiometrische Mengen Ti(OCHMe2)4 zugesetzt werden. Es besteht eine lineare Beziehung zwischen den Enantiomerenreinheiten von Hilfsstoff und Produkt.

Ar‐BINMOLs with Axial and sp3Central Chirality – Characterization, Chiroptical Properties, and Application in Asymmetric Catalysis

“…[21] Since the report by Ohno and co-workers [22] on the enantioselective addition of diethylzinc to aldehydes using a Ti(OiPr) 4 complex with chiral bis(triflamide), extensive studies have been carried out based on the modification of bis(sulfamide), TADDOLs, and BINOLs. [23] Despite achievements made in the asymmetric addition of aldehydes, it is still necessary to develop new types of catalytic systems and probe how the chiral catalysts work for the model reaction of diethylzinc with aldehyde, including asymmetric amplification [24] and asymmetric autocatalysis. [25] To further study the asymmetric induction of ArBINMOLs in this fundamental organic transformation, we have carried out the asymmetric 1,2-addition of diethylzinc to aldehdyes catalyzed by a combination of Ar-BINMOLs and Ti(OiPr) 4 .…”

TADDOLs, Their Derivatives, and TADDOL Analogues: Versatile Chiral Auxiliaries

“…It is hardly necessary to add that the only applications worth considering are ones for which, in homogeneous solution, there are no nonlinear effects (NLE) attributable to the involvement of more than one catalyst molecule in the rate-determining step. [379] This is a condition fulfilled by the titanium TADDOLate catalyzed addition of R 2 Zn to aldehydes [380] (Scheme 12) and the [32] cycloaddition of nitrones, [71] but not by the Diels ± Alder reaction of enoyloxazolidinones. [71,113,381] Finally, ease of utilization requires that the particles of an immobilized catalyst not be too small, for which reason our conditions for suspension polymerization have been so adjusted that spheres with a diameter of approximately 400 mm are preferentially formed.…”

“…As noted, nucleophilic additions to aldehydes-apart from allylations with CpTi-TADDOLate (Scheme 13)-proceed with maximum enantioselectivity only if excess (iPrO) 4 Ti is added along with titanium TADDOLate [380] (also true for use of BINOLate [392,393] and CYDISate; [243,245,247] see the examples in Scheme 25). This means on one hand that the corresponding chiral titanates are much more active as catalysts than achiral titanate (factors of over 1000:1 have been estimated), but also that the chiral systems require the presence of the latter for optimum activity.…”

“…The example of the titanium TADDOLate demonstrates that, under standard conditions (Et 2 Zn, PhCHO, toluene, À 25 8C, 0.2 equiv Ti ¥ 1-ate, 1.2 equiv (iPrO) 4 Ti)), there is a linear correlation between the enantioselectivity of TADDOL and that of the product. [71,380] approximately 10, that of CF 3 SO 2 NH 2 is approximately 6). With titanium BINOLate, which generally affords less selectivity in alkylzinc addition to aldehydes relative to CYDISate and TADDOLate (see also Scheme 1), the presence of excess (iPrO) 4 Ti also leads to better results than those achieved in the absence of achiral Lewis acid.…”

TADDOLe, ihre Derivate und Analoga – vielseitige chirale Hilfsstoffe

“…Chem. 2001, 113, 96 ± 142 hinzuweisen, dass nur solche Anwendungen infrage kommen, bei denen in homogener Lˆsung kein nichtlinearer Effekt (NLE) auftritt, der darauf beruht, dass mehr als ein Katalysatormolek¸l am geschwindigkeitsbestimmenden Schritt beteiligt ist, [379] eine Bedingung, die f¸r die Ti-TADDOLatkatalysierte R 2 Zn-Addition an Aldehyde [380] (Schema 12) und f¸r die [32]-Cycloaddition von Nitronen, [71] nicht aber f¸r die Diels-Alder-Reaktion von Enoyloxazolidinonen [71,113] erf¸llt ist. [381] Schlie˚lich gebietet die einfache Handhabung der immobilisierten Katalysatoren, dass die Partikel nicht zu klein sind, weshalb wir die Bedingungen bei der Suspensionspolymerisation so einrichteten, dass bevorzugt K¸gelchen von ca.…”