Diazadienes as Controlling Ligands in Catalysis, 5¹⁾. Synthesis of Chiral Diazadienes R^* – N = CR' – CR' = N – R^*

Abstract

The condensation of glyoxal (as hydrate) or 2,3-butanedione with primary amines is, in principle, a simple reaction. Unfortunately, aliphatic amines with secondary or tertiary a-carbons often give unwanted addition products. Under special reaction conditions the desired diimines (diazadienes (dad): R*-N = CR'-CR'= N -R*, R' = H, CH,) 4, and 6 -8 are obtained from (R)-1-phenylethylamine (1) and (lS,2S,3S,SR)-3-(aminomethyI)pinane (2). Depending on the dione, a morpholine morpholine 9 and a bioxazolidine 10 are formed from (S)-2-amino-l-butanoI (3), which are bound by electron-rich metals in their isomeric dad form ((dad)Mo(CO), 11 and 12). The acyclic dad structure is stabilized by 0-silylation (14, 15). The (dad)iron(O) catalyzed dimerization of butadiene with these controlling ligands to 4-vinyl-1-cyclohexene occurs with an enantiomeric excess up to 16%. Diazadiene als Steuerliganden in der Katalyse, 5 1) Synthese chiraler Diazadiene R*-N = CR'-CR'= N -R* Die im Prinzip einfache Kondensationsreaktion von Glyoxal (als Hydrat) und 2,3-Butandion mit primaren Aminen fiihrt leider bei aliphatischen Aminen mit tertiarem bzw. sekundarem a-Kohlenstoff oftmals zu unerwiinschten Additionsprodukten. Unter speziellen Synthesebedingungen kdnnen mit (R)-1-Phenylethylamin (1) und (lS,2S,3S,SR)-3-(Aminomethyl)pinan die gewiinschten Diimine (Diazadiene (dad): R*-N = CR'-CR'= N -R*, R' = H, CH,) 4, 6 -8 erhalten werden. Aus (S)-2-Amino-l-butanoI (3) werden je nach Dion-Komponente ein Morpholinomorpholin 9 bzw. ein Bioxazolidin 10 gebildet, die von elektronenreichen Metallen in ihrer isomeren Form als Diazadiene gebunden werden ((dad)Mo(CO), 11 und 12). Die offenkettige dad-Form ist durch 0-Silylierung (14, 15) stabilisierbar. Die (dad)Eisen(O)-katalysierte Dimerisierung von Butadien zu 4-Vinyl-1-cyclohexen mit diesen dad-Liganden ergibt Enantiomereniiberschiisse e.e. bis zu 16%.

A New Efficient Synthesis of (R,R)-2,2′-Bipyrrolidine: An Interesting Chiral 1,2-Diamine withC2 Symmetry

“…Aminals of (R,R)-2,2'-bipyrrolidine, which contains two nitrogen atoms in five-membered rings, are good examples of such a conformational restriction. (R,R)-2,2'-bipyrrolidine (9) was first prepared by Hirama and co-workers, by resolution with tartaric acid. [5] Another synthesis has been reported by Kotsuki et al, starting from mannitol or tartaric acid.…”

“…The first steps are based on the chiral diamine synthesis reported by Neumann et al, [7] latterly improved by Savoia and co-workers, [8] which starts from N,N-bis[(S)-1-phenylethyl]ethanediimine (5; Scheme 2). [9] O O N N By this method, N,N-bis[(S)-1-phenylethyl]-(R,R)-4,5-diamino-1,7-octadiene (6) is obtained in good yield (60 %) and excellent diastereoselectivity (> 99 %) when isolated and purified. Alternatively, a simple acid ± base washing procedure afforded a quantitative yield of material suitable for further transformation.…”

“…This synthesis of (R,R)-2,2'-bipyrrolidine (9) could be carried out on a large scale (0.4 mol) in 61 % overall yield, starting from 6 and using only acid ± base wash purifications and a final distillation, with an ee value of > 99 % (the ee value was determined by 31 P NMR spectroscopy). [12] With (R,R)-2,2'-bipyrrolidine (9) in hand, we easily prepared the corresponding aminals 10 with several aldehydes, [13] by simple stirring of the diamine with the aldehyde, in diethyl ether at room temperature (Scheme 4). None of the reactions however, gave products suitable for X-ray crystallography.…”

Enantioselective copper catalysed 1,4-conjugate addition reactions using chiral N-heterocyclic carbenes

“…In this case, attempted synthesis of the bisimine 40 by the acid catalysed route described above (Conditions A) [49] was unsuccessful and led to a complex mixture of products, from which the desired bisimine could not be separated. Instead, it was possible to form compound 40 in high yield by simply mixing the chiral amine and glyoxal in dichloromethane for 5 h (Conditions B) [29].…”

“…In addition, attempts to carry out counter anion exchange from BF À 4 to Cl À proved to be fruitless; it appears that this reaction can only be carried out in the opposite direction. It was, however, possible to prepare the compounds using a modified, two step procedure via the intermediate bis-imines (27 and 28) which were formed in excellent yield from the reaction between 2 equivalents of a chiral amine with glyoxal under acid mediated conditions (Scheme 8) [49].…”