Guanidine axially chiral

Enantioselective a-animation of carbonyl compounds has been promoted by l-azetidinecarboxylic acid,159 axially chiral guanidine derivative,160 and chiral palladium complexes.161... 

The axially chiral guanidine catalyst (155) (0.4-5 mol%) has been developed to facilitate the highly enantioselective Michael addition of 1,3-dicarbonyl compounds (g to a broad range of conjugated nitroalkenes (<98% ee).211... 

Axially chiral guanidines with an external guanidine unit such as dinaphthoazepineamidine are effective catalysts for the enantioselective addition of p-oxoesters and a 1,3-diketone to di-ferf-butyl azodicarboxylates to yield cx-hydrazino-p-oxoesters and a-hydrazino-p-dike-tones in 54-99% yields and in 15-98% ee [44]. For example, stirring 2-oxocyclopenta-necarboxylate and di(tert-butyl) azodicarboxylate in THF in the presence of 0.05 mol% catalyst for four hours at —60° C provides an adduct in quantitative yield and in 97% ee (Scheme 4.15). The (R)-catalyst was prepared from (/ )-2,2 -dimethyl-3,3 -binaphthalene-diol ditriflate, 4-methoxyphenylboronic acid and 3.5-di(rert-butyl)phenylboronic acid in six steps. 

An axially chiral and highly hindered binaphthyl-derived guanidine catalyst 18a with an internal guanidine unit (Figure 4.6) facilitates the highly enantioselective 1,4-addition... 

Figure 4.6 The structures of representative axial chiral guanidines 78 with an internal...

Terade, M., Nakano, M. and Uhe, H. (2006) Axially chiral guanidine as highly active and enantioselelctive catalyst for electrophilic amination of unsymmetrically substituted 1,3-dicarbonyl compounds. Journal of the American Chemical Society, 128, 16044-16045. 

Terada, M., Ikehara, T. and Ube, H. (2007) Enantioselective 1,4-addition reactions of diphenyl phosphite to nitroalkenes catalysed by an axially chiral guanidine. Journal of the American Chemical Society, 129, 14112-14113. 

Most recently, Terada and co-workers [132] realized the first organocatalytic asymmetric direct vinylogous Michael addition of a-tert-butylthio-substituted furanones to nitroalkenes. The reaction was catalyzed by axially chiral guanidine 133, leading to densely functionalized y-butenolides 130a in high iy/j-diastereo- and enantioselectivities. However, no example has showed for the unsubstituted -y-butenolide (Scheme 5.65). 

Both chiral tertiary amine-(thio)ureas 20 [39] and 21 [40] have been able to catalyze the a-amination of 3-ketoesters in excellent yields and high enantioselec-tivity. In these reactions, cyclic 3-ketoesters performed optimum while the acyclic counterparts reacted very slowly, giving very low ee. A transition state model involving dual activation of substrates is supported by DFT calculations [42]. The axially chiral guanidine 22 is another highly active catalyst for a-amination of various cyclic and acyclic 1,3-dicarbonyl compounds. 

The axially chiral guanidine base (231) has been employed to catalyse the viny-logous Michael addition of a-thio substituted fiiranones (229) to nitroalkenes. The resulting a,K-functionalized butenolides (230) were obtained with <99 1 dr and ... 

M. Terada, K. Ando, Enantioselective direct vinylogous Michael addition of functionalized furanones to nitroalkenes catalyzed by an axially chiral guanidine base, Org. Lett. 13 (2011) 2026-2029. 

Terada et al reported axially chiral guanidine (23) as a catalyst for the Michael reaction of malonate to nitroalkenes (Scheme 2.64) [124]. 

Electrophilic amination of 1,3-dicarbonyl compounds were catalyzed by an axially chiral seven-membered guanidine (24) with low catalyst loading (Scheme 2.65) [125]. 

To overcome the difficulty associated with the design of chiral guanidines as a catalyst, the binaphthyl-derived 22 was initially developed with the expectation that substituents at the 3,3 -positions of the binaphthyl backbone would break the planar symmetry of the guanidine skeleton to create an attractive chiral environment. This type of axially chiral organic base catalyst, particularly 22a, could indeed... 

In a related study, the same researchers used guanidine 52 for the enantioselective vinylogous Michael reaction of furanone 53 with various aromatic and aliphatic nitroalkenes (Scheme 10.50) [143]. In addition, several additional asymmetric transformations catalyzed by axially chiral guanidines were reported by Terada and coworkers between 2009-2012 (Schemes 10.51-55) [144-148]. 

Terada and coworkers reported, in 2010, an enantioselective, direct vinylogous aldol reaction of furanone derivatives with aromatic aldehydes catalyzed by axially chiral guanidines (Scheme 10.49) [142]. Initial catalyst screening revealed that both the bulkiness and the electronic nature of the G substituent on the guanidine had a large influence on catalyhc activity as well as enantio- and diastereoselectivity. 

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