A Catalytic System Consisting of Vanadium, Chlorosilane, and Aluminum Metal in the Stereoselective Pinacol Coupling Reaction of Benzaldehyde Derivatives

Pinacol Coupling Reaction of Aromatic Aldehydes Mediated by Aqueous Vanadium(II) Solution Under Ultrasound Irradiation

“…Based on these experimental results together with corresponding literature, [9,17] a plausible single-electron transfer (SET) mechanism was proposed as indicated in Scheme 2. The initial radical A was generated via a SET process between V(II) and ArCHO.…”

“…Mediated by vanadium(II), the coupling of some aromatic aldehydes was carried out in good yield. For example, mediated by vanadium(II) under sonication, 2a and 2h were prepared in 91% and 89% yields within 15 min and 30 min respectively; whereas meditated by the VOCl 3 /Me 3 SiCl/Al system and stirred for 24 h and 48 h, [9] the coupling of 1a and 1h afforded 2a and 2h in 68% and 49% yields respectively.…”

“…reported the stereoselective coupling of two different yet electronically similar aldehydes employing the well-characterized vanadium(II) complex, [V 2 Cl 3 (THF) 6 ] 2 [Zn 2 Cl 6 ]; the major diastereomer in all of the cross coupling reactions is a threo diol. [7] Hirao et al reported highly diastereoselective pinacol coupling of secondary aliphatic aldehydes induced by Cp 2 VCl 3 /R 3 SiCl/Zn, [8] and using VOCl 3 / Me 3 SiCl/Al system, [9] six aromatic aldehydes gave desired pinacols in 49-89% yields. Their diastereoselectivities were high (dl : meso !…”

Enantioselective pinacol coupling reaction of aromatic aldehydes catalyzed by chiral vanadium complexes

“…Recent investigations showed that the type of salan ligands displayed superior asymmetric induction over salen ligands in some reactions [27][28][29][30][31]. On the other hand, although the applications of vanadium compounds in pinacol coupling reaction had been well documented [7][8][9][10], to our knowledge, no chiral vanadium complexes have been used in the reaction in an enantioselective way. Herein we describe the highly asymmetric pinacol coupling of aromatic aldehydes catalyzed by chiral salan-VO(acac) 2 complexes.…”

“…Among various methods explored, the asymmetric pinacol coupling reaction provides a direct way by transforming the achiral aldehydes into chiral 1,2-diols. Although a variety of metals [2][3][4][5][6][7][8][9][10][11][12][13][14][15] had been exploited extensively in the pinacol coupling reaction, these utilizations were mainly focused on the diastereoselective way. Given the fact that both high diastereoselectivity and enantioselectivity should be considered for a successful asymmetric pinacol coupling reaction, this formidable challenge highlights the demand for an efficiently catalytic system.…”