Abstract
A series of 18 regio- and stereo-chemically diverse chiral non-racemic 1,2-, 1,3-, and 1,4-diamines have been synthesized from commercial (1S)-(+)-ketopinic acid and (1S)-(+)-10-camphorsulfonic acid. The structures of the diamines are all based on the d-(+)-camphor scaffold and feature isomeric diversity in terms of regioisomeric attachment of the primary and the tertiary amine function and the exo/endo-isomerism. Diamines were transformed into the corresponding noncovalent bifunctional thiourea organocatalysts, which have been evaluated for catalytic activity in the conjugative addition of 1,3-dicarbonyl nucleophiles (dimethyl malonate, acetylacetone, and dibenzoylmethane) to trans-β-nitrostyrene. The highest enantioselectivity was achieved in the reaction with acetylacetone as nucleophile using endo-1,3-diamine derived catalyst 52 (91.5:8.5 er). All new organocatalysts 48–63 have been fully characterized. The structures and the absolute configurations of eight intermediates and thiourea derivative 52 were also determined by X-ray diffraction.
Highlights
In the field of asymmetric synthesis and catalysis, camphor derivatives have found their application as efficient chiral auxiliaries i.e. camphorsultam [7,8] and as ligands in metal-catalyzed reactions, as exemplified by DAIB [9] and MIB [10] used for the addition of organozinc reagents to aldehydes
Appeared in 2005 [15], shortly after the first seminal works at the turn of the millennium reported by List, Barbas, and Lerner [16], MacMillan [17], Jacobsen [18,19] and Takemoto [20], and Enders and Kallfass [21]
Within our continuing study on camphor-based diamines as potential organocatalyst scaffolds with camphor as the exclusive chiral framework, we previously reported on camphor C2, C3, and with camphor as the1,2, exclusive framework, previously reported on camphor
Summary
In the field of asymmetric synthesis and catalysis, camphor derivatives have found their application as efficient chiral auxiliaries i.e. camphorsultam [7,8] and as ligands in metal-catalyzed reactions, as exemplified by DAIB [9] and MIB [10] used for the addition of organozinc reagents to aldehydes. In the field of asymmetric organocatalysis [11,12], camphor-derived organocatalysts [13,14]. With respect to the structure of camphor-derived organocatalysts, they can be divided into two groups (Figure 1) [13]. The largest group of camphor-derived organocatalysts are mostly covalent bifunctional catalysts characterized
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