Enantioselectivity cyclic imine

Groeger, H., Saida, Y., Arai, S., Martens, J., Sasai, H., and Shibasaki, M., First catalytic asymmetric hydrophosphonylation of cyclic imines highly efficient enantioselective approach to a 4-thiazolidinylphosphonate via chiral titanium and lanthanoid catalysts,Tetrahedron Lett., 37, 9291, 1996. 

Table 6.5 Enantioselective hydrogenation of cyclic imines catalyzed by [(R,R,R)-(EBTHI)TiX2],...

Cyclic imines do not have the problem of syn/anti isomerism and therefore, in principle, higher enantioselectivities can be expected (Fig. 34.8). Several cyclic model substrates 6 were hydrogenated using the Ti-ebthi catalyst, with ee-val-ues up to 99% (Table 34.5 entry 5.1), whereas enantioselectivities for acyclic imines were <90% [20, 21]. Unfortunately, these very selective catalysts operate at low SCRs and exhibit TOFs <3 h-1. In this respect, iridium-diphosphine catalysts, in the presence of various additives, seem more promising because they show higher activities. With several different ligands such as josiphos, bicp, bi-... 

Table 34.5 Selected results for the enantioselective hydrogenation of cyclic imines (for structures, see Fig. 34.8) Catalytic system, reaction conditions, enantioselectivity, productivity and activity.

Particularly noteworthy is the discovery of a new type of the active catalyst 99,103,104 a crystalline, air-stable yellow-orange solid, which can serve as a highly enantioselective tool in the titanium-catalyzed hydrosilylation of imines. The reaction can be highly stereoselective for both acyclic and cyclic imines under a wide range of hydrogen pressures (Scheme 6-46). 

TABLE 9.33. ENANTIOSELECTIVE ADDITION OF ALLYLZINC REAGENTS TO CYCLIC IMINES ... 

Highly enantioselective hydrogenation of geometry-fixed cyclic imines has been achieved by the use of certain chiral Ti and Ir catalysts [14,17]. In particular, a chiral titanocene catalyst developed by Buchwald possess excellent enanti-odifferentiating ability for a variety of cyclic substrates [18]. 

The activity and enantioselectivity of chiral Ir catalysts have been tested by using 2,3,3-trimethylindolenine as a model substrate. Hydrogenation of the cyclic imine with [Ir(bdpp)Hl2 2 gives the corresponding chiral amine with 80% ce (Scheme 1.99) [350]. The stereoselectivity is somewhat better than that with acyclic substrates (see Scheme 1.94). A neutral BCPM-Ir complex with Bil3 effects asymmetric hydrogenation in 91% optical yield [354], A complex of MCCPM shows similar enantioselection [354], These complexes are not applicable to the reaction of other acyclic and six-membered cyclic imines. An MOD-DIOP-Ir complex is also usable with the aid of ( -C4H9)4NI [355], An Ir complex of BICP with phthalimide effectively... 

Asymmetric transfer hydrogenation of cyclic imines and iminiums in water was carried out in high yields and enantioselectivities with sodium formate as the hydrogen source and CTAB as an additive, catalysed by a water-soluble and recyclable ruthenium(II) complex of the ligand (23).371... 

The hydrophosphonylation of cyclic imines (thiazolines) has also been reported.69 Representative results are shown in Table 14. For example, reaction of 150 with dimethyl phosphite in the presence of 20 mol % of LPB gave 151 in only modest yield (53%) and enantioselectivity (Table 14, entry 1). The rate of the... 

Chiral sodium acyloxy borohydride 554 prepared from NaBH4 and AyV-phthaloyl amino acid reduced cyclic imines in good enantioselectivity. Thiazazincolidine complex 555 was shown to be an excellent catalyst for the catalytic reduction of dihydroisoquinolines with BH3-THF (Equation (265)).1132-1134... 

Kong, K., Moussa, Z. and Romo, D., 2005. Studies toward a marine toxin immunogen enantioselective synthesis of the spiro-cyclic imine of (-)-gymnodimine. Org Lett 7, 5127-5130. 

A-diphenylphosphinoyl imines also react with dialkylzinc in the presence of stoichiometric or catalytic amounts of different chiral (see Chiral) ligands (Scheme 24). Acid hydrolysis of the resulting phosphinamides occms without racemization and gives enantiomerically enriched primary amines. The allylation of various cyclic imines was obtained with high enantioselectivity (see Electrophile), 77 to 99% e.e., in the presence of lithiated bis-oxazoline ligands (Scheme 25). 

The organolanthanide-catalyzed alkene hydroamination has been reported. With this approach, amino alkenes (not enamines) can be cyclized to form cyclic amines, and amino alkynes lead to cyclic imine. The use of synthesized C-1 and C-2 symmetric chiral organolanthanide complexes give the amino alcohol with good enantioselectivity. 

Heterobimetallic catalysis mediated by LnMB complexes (Structures 2 and 22) represents the first highly efficient asymmetric catalytic approach to both a-hydro and c-amino phosphonates [112], The highly enantioselective hydrophosphonylation of aldehydes [170] and acyclic and cyclic imines [171] has been achieved. The proposed catalytic cycle for the hydrophosphonylation of acyclic imines is shown representatively in Scheme 10. Potassium dimethyl phosphite is initially generated by the deprotonation of dimethyl phosphite with LnPB and immediately coordinates to the rare earth metal center via the oxygen. This adduct then produces with the incoming imine an optically active potassium salt of the a-amino phosphonate, which leads via proton-exchange reaction to an a-amino phosphonate and LnPB. 

The enantioselective total synthesis of the Securienega alkaloid (-)-phyllanthine by S.M. Weinreb et al. involved a stereoselective Yb(OTf)3-promoted hetero Diels-Alder reaction between a cyclic imine dienophile and Danishefsky s diene This was the first example of using an unactivated cyclic imine in this type of cycloaddition. Commonly used Lewis acid catalysts (e.g., SnCb, TiCU, etc.) produced only low yields of the desired cycloadduct. However, it was discovered that ytterbium triflate catalyzed the cycloaddition and afforded the product in 84% yield. Later they also found that the cyclization could occur at high pressure and in the absence of the catalyst, although a slightly lower yield (71%) of the product was obtained. 

Hydrosilylation of unsaturated organic molecules is an attractive organic reaction. Asymmetric hydrosilylation of prochiral ketones or imines provides effective routes to optically active secondary alcohols or chiral amines (Scheme 756). These asymmetric processes can be catalyzed by titanium derivatives. The ( A ebthi difluoro titanium complex has been synthesized from the corresponding chloro compound.1659 This compound results in a very active system for the highly enantioselective hydrosilylation of acyclic and cyclic imines and asymmetric hydrosilylation reactions of ketones including aromatic ketones.1661,1666,1926-1929 An analogous l,l -binaphth-2,2 -diolato complex catalyzes the enantioselective hydrosilylation of ketones.1... 

Ti Extremely selective for cyclic imines. Catalysts are extremely air and moisture sensitive. Enantioselectivity depends on the E/Z purity of the starting imine. 

Enantioselective Reduction of Cyclic Imines (C=N Group Endocyclic)... 

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