Modified guanidines as chiral superbases: application to asymmetric Michael reaction of glycine imine with acrylate or its related compounds

Ishikawa, Tsutomu; Araki, Yusuke; Kumamoto, Takuya; Seki, Hiroko; Fukuda, Keiko; Isobe, Toshio

doi:10.1039/b009193f

Cited by 155 publications

(41 citation statements)

References 15 publications

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“…7,11) A 1,3-disubstituted (4S,5S)-diarylimidazolidine skeleton 23 with an (R)-1-(2-hydroxymethyl)-2-phenylethylimino moiety at the 2 position (or the enantiomer), which can be prepared using method I, was found to be the most effective catalyst in these reactions, in which an (R)-excess adduct 24 was obtained. Treatment with ethyl acrylate (22a) as a vinyl compound in the presence of catalyst 23a [designated as "(ϩ)-Chiba-G"] smoothly afforded the adduct 24a (97% ee in 85% yield) when the reaction was carried out without solvent (for 3 d), whereas a less effective reaction (79% ee in 15% yield) was observed in tetrahydrofuran (THF) solution (for 7 d).…”

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confidence: 99%

“…Treatment with ethyl acrylate (22a) as a vinyl compound in the presence of catalyst 23a [designated as "(ϩ)-Chiba-G"] smoothly afforded the adduct 24a (97% ee in 85% yield) when the reaction was carried out without solvent (for 3 d), whereas a less effective reaction (79% ee in 15% yield) was observed in tetrahydrofuran (THF) solution (for 7 d). 7) Interestingly, replacement of the acrylate 22a with methyl vinyl ketone (22b) led to higher asymmetric induction in THF (96% ee in 90% yield) than without solvent (80% ee in 90% yield). In general, remarkable rate acceleration was observed in solventless reactions.…”

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confidence: 99%

“…It is theoretically possible to introduce five chiral centers in the guanidine system. We found that modified guanidines prepared using our original methods [4][5][6] were effective not only in catalytic [7][8][9][10][11][12][13] but also in stoichiometric asymmetric syntheses. 14,15) The concept of modified guanidines as chiral auxiliaries in asymmetric synthesis is illustrated in Chart 2, [16][17][18] in which reactive, but resonance-stabilized, guanidinium salts 5 could be produced from guanidines 4 by quarternarization with a reagent (A-B).…”

Section: Modified Guanidines As Chiral Auxiliaries (Functionality As mentioning

confidence: 99%

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Guanidine Chemistry

Ishikawa

2010

Chem. Pharm. Bull.

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Guanidines are categorized as strong organobases; however, their catalytic utility in organic synthesis has not been discussed thoroughly. The author's group has extensively and systematically studied their potential ability focusing on: 1) modified guanidines as chiral auxiliaries; 2) guanidinium ylides for aziridine formation; 3) the affinity of bisguanidine for proton and metal salts; and 4) the potential chirality of bisguanidine. Under the first topic, a variety of chiral guanidines was designed by the introduction of chirality on the three guanidinyl nitrogens, and the modified guanidines prepared using our original methods were found to be effective not only in catalytic but also in stoichiometric asymmetric syntheses. Under the second topic, the reaction of guanidinium salts carrying a glycinate function with aromatic or unsaturated aldehydes under basic conditions unexpectedly afforded aziridine-2-carboxylates, which were available as useful building blocks in organic synthesis due to their convertibility to functionalized amino acid derivatives in the ring-opening reaction, together with urea compounds recyclable to the starting guanidinium salts. The introduction of a chiral template to the guanidinium salt allowed us to expand the cyclic aziridination reaction to an asymmetric version. Under the third topic, effective complexabilty of bisguanidines with either proton or metal ions in water was observed, suggesting their possible application to the removal of toxic substances from polluted water and recovery of rare elements as material sources. Under the final topic, monomethylation or monoethylation of bisguanidine afforded a chiral product via asymmetric crystallization, indicating that bisguanidines have a potential chiral character due to the plane asymmetry.

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confidence: 99%

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confidence: 99%

Section: Modified Guanidines As Chiral Auxiliaries (Functionality As mentioning

confidence: 99%

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Guanidine Chemistry

Ishikawa

2010

Chem. Pharm. Bull.

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“…19 In addition, asymmetric PTC Michael addition reactions have been performed using other chiral ammonium salts derived from L-tartrate 20 and (S)-BINOL, 21 both achieving moderate enantioselectivities. Moreover, chiral guanidines from (R)-1-phenylethanamine have also been used although achieving low ee's, 22 much better results being achieved using guanidines from C 2 -symmetric 1,2-diphenylethane-1,2-diamines 23 or even a chiral crown ether from chiro-inositol. 24 We have recently prepared dimeric ammonium salts derived from cinchonidine or cinchonine and a bridging (anthracen-9,10-yl)dimethyl moiety, 3a,d and 4a,d respectively, which have shown good enantioselection as catalysts in the PTC alkylation of benzophenone imine glycinates.…”

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Enantioselective Michael reactions promoted by recoverable dimeric anthryl-derived Cinchona phase-transfer catalysts

Chinchílla¹,

Mazón²,

Nájera³

et al. 2005

Arkivoc

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“…9) In this communication, we report the catalytic asymmetric Michael reaction of a glycine Schiff base using bis-ammonium salts as PTCs. [10][11][12][13][14][15][16] Binaphthol and its derivatives are known to be a versatile starting compound for the preparation of chiral catalyst. And also the functionalization of 2, 3 and 6 positions could provide a various analogues for each asymmetric transformation.…”

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Asymmetric Michael Reaction Promoted by New Chiral Phase-Transfer Catalysts

Arai

Tokumaru

Aoyama

2004

CHEMICAL & PHARMACEUTICAL BULLETIN

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A catalytic asymmetric Michael reaction promoted by new chiral quaternary ammonium salts is described. The products are obtained with moderate ee (up to 75% ee), and the enantioselectivity is strongly dependent on both the substituents on the aromatic rings and the ammonium moiety in the catalysts.Key word asymmetric synthesis; chiral ammonium salt; phase-transfer catalysis; Michael reaction Phase-transfer catalysts (PTCs) offer many advantages as organic reagents for the transformation of organic molecules, including mild reaction conditions (water can be used as a solvent), simple reactions, environmental benign and low cost, and they have recently been considered to be a useful tool in the development of green chemistry. In particular, onium salts have been recognized as one of the most powerful PTCs due to their facile preparation and structural diversity, and their utility in asymmetric synthesis has been investigated. The first successful examples of asymmetric catalysis with a chiral ammonium salt as a PTC were reported independently by Dolling 2) and O'Donnell 3) in the mid-to late 1980's. The catalysts they have reported for use in enantioselective alkylation are both cinchona alkaloid derivatives. These two pioneering examples in asymmetric PTC chemistry have been applied to other asymmetric reactions. [4][5][6] On the other hand, Maruoka and co-workers reported excellent results in the asymmetric alkylation of glycine Schiff base using designer ammonium salts. 7) Belokon and Kagan also achieved high enantioselectivities using nickel complexes as PTCs.8) Nagasawa and co-workers reported chiral guanidinium salts as a new type of PTC that promoted O'Donnell's alkylation under PTC conditions. 9) In this communication, we report the catalytic asymmetric Michael reaction of a glycine Schiff base using bis-ammonium salts as PTCs. [10][11][12][13][14][15][16] Binaphthol and its derivatives are known to be a versatile starting compound for the preparation of chiral catalyst. And also the functionalization of 2, 3 and 6 positions could provide a various analogues for each asymmetric transformation. Moreover, bis-ammonium salts would be expected to accelerate the reaction due to the two reaction site and it would prevent the undesired reaction pathway which chiral PTCs do not concern. Based upon these, we started to investigate the preparation of symmetrical bis-ammonium salts and survey the asymmetric Michael reaction. First of all, we begun to prepare the 2,3-disubstituted binaphthyl and transformed to bis ammonium salt, as outlined in Chart 1. Di-MOM ether of (S)-BINOL 1 was formylated at the 3,3Ј-position and subsequent deprotection of MOM groups by treatment with acid gave 2 in 65% yield. Benzylation of the phenolic function of 2 with 4-trifluoromethylbenzyl bromide, reduction of the formyl groups and subsequent halogenation of the resulting primary diol with CBr 4 -PPh 3 gave the corresponding bis(bromomethyl)binaphthyl 5 in 68% overall yield. Quaternarization of 5 with triethylamine under reflux condition...

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Modified guanidines as chiral superbases: application to asymmetric Michael reaction of glycine imine with acrylate or its related compounds

Cited by 155 publications

References 15 publications

Guanidine Chemistry

Guanidine Chemistry

Enantioselective Michael reactions promoted by recoverable dimeric anthryl-derived Cinchona phase-transfer catalysts

Asymmetric Michael Reaction Promoted by New Chiral Phase-Transfer Catalysts

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