Revisiting optically active quaternary derivatives made from prolinol as phase transfer catalysts
摘要:
New non-racemic ammonium salts derived from prolinol have been prepared which are stereogenic both at N and at C. Absolute configurations rest on X-ray structures for 3c and 7a. The new compounds have been tested in a number of known enantioselective phase transfer catalytic (PTC) reactions to gain insight into steric control factors in such processes. Only very moderate e.e.s were observed. A SAMP hydrazone related catalyst (7a) reported by other authors was fully characterized. Racemic reaction products were obtained in two alkylations of diphenylmethylene benzylimine in the presence of this pure catalyst 7a. Very high e.e.s reported previously by others could not be reproduced. (C) 1998 Elsevier Science Ltd. All rights reserved.
An optically active .beta.-aminoalkoxyborane complex of the formula (I): ##STR1## wherein R.sup.1 is C.sub.1 -C.sub.8 alkyl, C.sub.3 -C.sub.7 cycloalkyl, C.sub.7 -C.sub.11 aralkyl or C.sub.6 -C.sub.10 aryl, R.sup.2 is hydrogen, C.sub.1 -C.sub.8 alkyl, C.sub.3 -C.sub.7 cycloalkyl or C.sub.7 -C.sub.11 aralkyl, or R.sup.1 and R.sup.2 together form (CH.sub.2).sub.n wherein n is 3 or 4, and Ar is naphthyl, anthryl or phenanthryl, which may be substituted by from 1 to 3 substituents selected from the group consisting of halogen, nitro, C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.7 cycloalkyl, C.sub.2 -C.sub.6 alkenyl, C.sub.2 -C.sub.6 alkynyl, C.sub.7 -C.sub.11 aralkyl, C.sub.6 -C.sub.10 aryl, C.sub.1 -C.sub.6 alkoxy and styrene polymer substituents.
1. An optically active .beta.-aminoalkoxyborane complex of the formula (I): ##STR1## wherein R.sup.1 is C.sub.1 -C.sub.8 alkyl, C.sub.3 -C.sub.7 cycloalkyl, C.sub.7 -C.sub.11 aralkyl or C.sub.6 -C.sub.10 aryl, R.sup.2 is hydrogen, C.sub.1 -C.sub.8 alkyl, C.sub.3 -C.sub.7 cycloalkyl or C.sub.7 -C.sub.11 aralkyl, or R.sub.1 and R.sup.2 together form (CH.sub.2).sub.n wherein n is 3 or 4, and Ar is naphthyl, anthryl or phenanthryl, which may be substituted by from 1 to 3 substituents selected from the group consisting of halogen, nitro, C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.7 cycloalkyl, C.sub.2 -C.sub.6 alkenyl, C.sub.2 -C.sub.6 alkynyl, C.sub.7 -C.sub.11 aralkyl, C.sub.6 -C.sub.10 aryl, C.sub.1 -C.sub.6 alkoxy and styrene polymer substituents.
Enantioselective addition of dialkylzinc reagents to N-(diphenylphosphinoyl)imines catalyzed by β-aminoalcohols with the prolinol skeleton
作者:Raquel Almansa、David Guijarro、Miguel Yus
DOI:10.1016/j.tetasy.2007.11.006
日期:2007.11
Several beta-aminoalcohols with the prolinol framework are shown to be very efficient catalysts for the enantioselective addition of dialkylzinc reagents to N-(diphenylphosphinoyl)imines. The use of 0.5 equiv of the catalyst leads to the expected addition products in good yields and with ee up to 94% in a reaction time of only 4 It at room temperature. This ee is the highest value reported so far using 0.5 equiv of an aminoalcohol as a promoter. High enantioselectivities are obtained in the addition of dialkylzincs to both aromatic and aliphatic imines. The amount of the catalyst can be reduced to 0.25 equiv with a slight decrease in the ee. A very interesting effect of the addition rate and temperature on the enantioselectivity was also observed. (c) 2007 Elsevier Ltd. All rights reserved.