Catalysed asymmetric reaction of aldehydes with dialkylzinc in the presence of chiral pyridyl alcohols as ligands

Effect of microwave heating in the asymmetric addition of dimethylzinc to aldehydes

“…Using ligand 1 in 10 mol% and 20 min irradiation time resulted in a considerable drop in yield (55%) but with a reasonable enantiomeric excess (83%) ( For the catalysis with ligand 2 at low temperature, the results by Pericàs and coworkers producing 4a in 87% yield and 94% ee in 24 h, in hexanes/toluene at 0°C, are almost unbeatable [8,22]. Aimed at testing the microwave-heating methodology we carried out conventional room temperature reactions in 1 h, to compare them with the microwave results in the same time at moderate temperature (75°C) ( Table 1, entries [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In some preliminary tests with benzaldehyde (3a), we noted that the use of only toluene as solvent improved the yields compared to the use of hexanes/toluene, so the reactions were made in toluene.…”

“…Since the initial report of Oguni and Omi in 1983 on the reaction of diethylzinc with benzaldehyde, with 49% enantioselectivity [4], and the synthetic breakthrough of Noyori and coworkers raising the enantioselectivity to 95% (using (À)-3-exo-dimethylaminoisoborneol as ligand) [5], the research on asymmetric organozinc additions to carbonyl compounds has continued receiving attention [6]. In spite of that, there are only very few examples reporting highly enantioselective asymmetric additions of dialkylzincs to aldehydes proceeding rapidly (20-30 min) [7,8]. Most of the published cases require longer reaction times, ranging from several hours to several days [1,[9][10][11].…”

A facile synthesis of 3 or 3,3′-substituted binaphthols and their applications in the asymmetric addition of diethylzinc to aldehydes

“…for (S)-1-(4 0 -chlorophenyl)-1-propanol [17]; [a] D +13.33 (c = 1.0, PhH) in 76% e.e. for (R)-1-(4 0 -bromophenyl)-1-propanol [18]; [a] D À34.6 (c = 5.0, PhH) in 90% ee for (S)-1-(4 0 -methoxyphenyl)-1-propanol [19]; [a] D À44.9 (c = 1, toluene) in 83% e.e. for (S)-1-(2 0 -methoxyphenyl)-1-propanol [20]; [a] D +45.5 (c = 0.8, CHCl 3 ) in 74% e.e.…”

Chiral Diselenides from Benzylamines: Catalysts in the Diethylzinc Addition to Aldehydes

“…GC (80+160" with 5Ojmin): 91 % ee. (CHCI,): 3604, 3444, 2968(CHCI,): 3604, 3444, , 2934(CHCI,): 3604, 3444, , 1463(CHCI,): 3604, 3444, , 1267(CHCI,): 3604, 3444, , 1178(CHCI,): 3604, 3444, , 1135(CHCI,): 3604, 3444, , 1049(CHCI,): 3604, 3444, , 1017 [12]. Colorless oil.…”