Enantioselective reductions of aromatic ketones with ammonia–borane complexes of chiral tetraphenyl-18-crown-6 derivatives

Abstract

Enantioselective reductions of prochiral aromatic ketones with adducts formed between ammonia-borane and (2Rr3R,1 1 R,12R)-and (2S,3Sr1 1 Sr12S)-tetraphenyl-1 ,4,7,10r13,16-hexaoxacyclo-octadecane, (RRRR)-( 3) and (SSSSI-(3), have afforded the corresponding (S) and ( R ) aromatic secondary alcohols with enantiomeric excesses of 2 0 -6 7 ' / o.

A 1:1 adduct between thetrans-cisoid-transisomer of 2,3,11,12-tetra-anisyl-18-crown-6 with the (RRRR)-configuration and ammonia–borane

“…Shahriari-Zavareh, Stoddart & Williams, 1984) using the ammonia-borane (BHaNH3) adducts of the chiral trans-transoid-trans-tetraphenyl-18-crown-6 deriva, tives (9)* gives added significance to a determination of the solid-state structure of these adducts. In this paper, we (a) describe the preparation of a 1:1 adduct between the trans-transoid-trans isomer (4) of (2R,3R,11R,12R)-tetra-anisyl-18-crown-6, (b) report on the determination of its crystal structure, and (c) compare the structural characteristics of [(4).BHaNH 3] with those already reported (Allwood et aL, 1984) for…”

“…In this paper, we (a) describe the preparation of a 1:1 adduct between the trans-transoid-trans isomer (4) of (2R,3R,11R,12R)-tetra-anisyl-18-crown-6, (b) report on the determination of its crystal structure, and (c) compare the structural characteristics of [(4).BHaNH 3] with those already reported (Allwood et aL, 1984) for…”

“…The NH 3 and BH 3 groups in the substrate are staggered with respect to each other, the smallest H-N-B-H torsion angle being 54 °. The NH 3 group in BH3NH 3 is hydrogen bonded to O(4), O(10) and O (16) (Allwood et al, 1984) for trans -transoidtrans-tetraphenyl-18-crown-6 (8). The similarity of the solid-state structures of these two 1:1 adducts is reassuring when one considers the potential roles (Stoddart, 1984(Stoddart, , 1987aColquhoun, Stoddart & Williams, 1986) of (4) and (8) as chiral auxiliaries and catalysts.…”

“…Together with the crystal structures also available for some of the diastereoisomers of 2,3,11,12-tetraphenyl-18-crown-6 (Weber, Sheldrick, Burgemeister, Dietl, Mannschreck & Merz, 1984;Blasius, Rausch, Andreetti & Rebizant, 1984) and their adducts with BH3NH 3 (Allwood et al, 1984), these data will provide a focal point for reference when we discuss (Allwood, Crosby, Koppenh6ffer, Pears, Shahriari-Zavareh, Slawin, Stoddart & Williams, 1988) the physical and chemical properties of these receptors and their BH3NH 3 adducts in solution.…”

Structure of the dextrorotatorytrans-cisoid-transisomer of 2,3,11,12-tetra-anisyl-18-crown-6: (2R,3R,11R,12R)-2,3,11,12-tetrakis(4-methoxyphenyl)-1,4,7,10,13,16-hexaoxacyclooctadecane

“…The corresponding parameters in [(7). (BH3NH3) 2] are (Allwood et al, 1984) 1.78 A and 24 ° There are no contacts of less than normal van der Waals distances between the 1:2 adducts.…”