A Neutral, Chiral, Bis(imidazolidine)‐Derived NCN‐Type Palladium Pincer Complex with Catalytic Activity

Chiral Bis(imidazolidine)‐Derived NCN Pincer Rh Complex for Catalytic Asymmetric Mannich Reaction of Malononitrile with N‐Boc Imines

“…In our studies on the asymmetric catalysis, sp 2 imine coordination of oxazoline was replaced with sp 3 amine coordination of imidazolidine for introducing a cooperative NH functionality adjacent to the metal center, and we have succeeded in the first development of a pincer bis(imidazolidine)‐derived NCNPd complex for a catalytic asymmetric Michael reaction of malononitrile with nitroalkenes 11. Herein, a new bis(imidazolidine)‐derived NCN–rhodium complex was prepared for asymmetric catalysis of malononitrile with N ‐ tert ‐butyloxycarbonyl ( N ‐Boc) imines.…”

“…Encouragedbythe first success in the synthesize of abis(imidazolidine)-derived palladium complex using al igand-introduction procedure, [11] the preparation of NCN-rhodium complex was tried in the similar conditions.…”

“…Although the presence of the corresponding NH protons The catalytic activities of the newly prepared NCN pincerR h complexes were examined in reactions by using malononitrile, because the previously developed bis(imidazolidine)-derived NCN-Pdc omplex wasf ound to be an efficient catalyst for conjugate addition of malononitrile to nitroalkenes. [11] Utilizing [PhBidine-Rh(OAc) 2 ], which wasg enerated quantitativelyb y treatment of [PhBidine-RhCl 2 ]w ith AgOAc, [4d] the reactionw as smoothly catalyzed at 0 8Ct og ive the product in 30 % ee (20 h, 99 %y ield). In as imilar conjugate addition of malononitrile to (E)-chalcone, thought he pincerR hCl 2 complexes were catalytically inactive, the use of 5mol %[ PhBidine-Rh(OAc) 2 ] gave the Michael adduct in 75 yield with 50 % ee (40 8C, 60 h), whereas 5mol %[ tBu-PhBidine-Rh(OAc) 2 ]g ave the product in 67 %y ield with 70 % ee.A mong the examined reactions, the Mannich reactiono fm alononitrile with N-Boc imines reported by Han and Pan et al…”

Asymmetric Michael Addition of Malononitrile with Chalcones via Rosin-Derived Bifunctional Squaramide

“…Substrate 3o with 4-Me substituent on both R 1 and R 2 phenyl reacted with malononitrile smoothly to afford the corresponding adduct with good yield and high enantioselectivity (70% yield and 86% ee, entry 15). Other chalcone analogues, such as 2-enoylpyridine 3p and 1-naphthlaldehyde derivative 3q, were also tested, both giving low results (entries [16][17]. The pyridine nitrogen of substrate 3p might involve the hydrogen bonding of the squaramide catalyst V in the H-bond framework to change the steric environment of the catalytic system, which made the activity of catalyst fade out, leading to lower reactivity and enantioselectivity [26].…”

“…The Michael reaction of carboanion nucleophiles to activated olefins represents a powerful type of the most remarkable transformations for the new carbon-carbon bond formation in modern organic synthesis, and has been immensely exploited over the past few decades [1][2][3][4][5][6][7]. Among the versatile nucleophiles, the employment of malononitrile for asymmetric Michael addition has received extensive attention since its nitrile group could be efficiently converted to valuable functionalities [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. To date, a few research groups have devoted their efforts to the catalytic asymmetric Michael reaction of malononitrile onto chalcones and their analogues, by either metal-catalytic [19,20] or organocatalytic [21][22][23][24][25][26][27] methods.…”