Functionalized BINOL Derivatives as Ligands for Enantioselectively Catalyzed Aldol Additions: Highly Enantioselective Synthesis of Chiral β‐Hydroxy Thioesters.

Abstract

Enantioselective syntheses O 0031 Functionalized BINOL Derivatives as Ligands for Enantioselectively Catalyzed Aldol Additions: Highly Enantioselective Synthesis of Chiral β-HydroxyThioesters. -A number of BINOL-derivatives of type (I) and (II) is prepared and examined in an asymmetric model reaction, the addition of S-ketene silyl acetal (II) to aldehydes (IIII). Best results are obtained with derivative (Ia) and various aldol products are obtained in excellent enantioselectivity. -(ZIMMER*, R.; SCHEFZIG, L.; PERITZ, A.; DEKARIS, V.; REISSIG, H.-U.; Synthesis 2004, 9,

Tandem RCM–Claisen Rearrangement–[2+2] Cycloaddition of O,O'-(But-2-en-1,4-diyl)-bridged Binaphthols

“…Column chromatography was performed on SiO 2 , 40-63 µm. Reported procedures have been followed to obtain 3,3′-disubstituted 2,2′-dihydroxy-1,1′-binaphthyl precursors 1b – d [ 48 , 49 , 50 , 51 , 52 ] and diallyloxy compound 2a [ 26 ].…”

Synthesis of Poly(Ethylene Glycol)–Supported (R)-BINOL Derivatives and Their First Application in Enantioselective Mukaiyama Aldol Reactions

“…A similar result (40% ee) was observed previously, where (R)-14 has been used as the only ligand in the aldol reaction of 1 and 2. [23] Gratifyingly, an excellent level of stereoselectivity could be obtained by the ligand combination (R)-6 =(S)-13, starting the aldol reaction at 0 C and then at room temperature, which clearly surpasses the uncombined ligand (R)-6 under the same reaction conditions (compare entry 10 in Table 1 and entry 15 in Table 2). Aldol reactions with aliphatic aldehydes (e.g., 2-phenylethanal and heptanal) using ligand (R)-6 under the reaction conditions as described in Table 1 provided the expected aldol products in high yields, but so far only with moderate enantioselectivity.…”

“…It is well known that combinations of BINOL derivatives with achiral and chiral promoters are useful in several asymmetric carbon-carbon bond-forming processes. [4,22,23,[29][30][31] These additives either enhance the enantioselectivity and=or the reactivity (chemical yield). Representative examples of these experiments are summarized in Table 2, which should be compared to the results without additives (entries 1 and 2).…”

“…[12] Reflecting the potential utility of the Mukaiyama process [13] in the synthesis of compounds of biological importance and based on the experience of other groups, [14][15][16][17][18][19][20][21] we have already reported an efficient method for enantioselective additions of S-ketene silyl acetal 2 to various carbonyl compounds employing a catalyst without polymer support. [22,23] In the present study, we focus our attention on the preparation of MPEG-supported BINOL ligands and their efficacy as BINOLate-titanium catalysts in enantioselective aldol reactions. As a model reaction, we have chosen the aldol reaction of S-ketene silyl acetal 2 with 2-styryl-oxazole-4-carbaldehyde (1), resulting in the enantioselective formation of aldol product 3, which is a known intermediate in the total synthesis of the marine natural product phorboxazole B [Eq.…”