Chiral complexes examples

An asymmetric version of this reaction was achieved by the use of complexes derived from chiral imidazolidinones. For example, the reaction of Danishefsky s diene with these chiral complexes occurs with both high exo endo selectivity and high facial selectivity at the dienophile [103] (Scheme 56). 

AT-heterocyclic carbene complexes of Pd(II) or Pd(0) were extensively used in various reactions and several groups have reported syntheses of chiral complexes [5]. However, only a few examples of asymmetric catalysis are... 

Examples of some Cl chiral complexes with octahedral coordination... 

Ampicillin (Fig. 2.4) provides a more complex example than adrenaline with regard to assignment of absolute configuration since it contains four chiral centres. 

Chart 2. Examples of chiral complexes studied in redox reactions with GO, HRP, and cytochrome c peroxidase. 

Both the ally lie alcohol and tert-hutyX hydroperoxide are achiral, but the product epoxide is formed in high optical purity. This is possible because the catalyst, titanium tetraiso-propoxide, forms a chiral (possibly dimeric [36]) complex with resolved diethyl tartrate [(+)-DET] which binds the two achiral reagents together in the reactive complex. The two enantiotopic faces of the allylic double bond become diastereotopic in the chiral complex and react at different rates with the tert-butyl hydroperoxide. Many other examples may be found in recent reviews [31, 37-39]. 

Finally, optical isomerism is even more rare. The first example of the determination of the absolute configuration of such a chiral complex is shown in Fig I2.15.26 This... 

The Cahn-Ingold-Prelog rules work for inorganic compounds too but coordination complexes often have coordination numbers greater then four and may exhibit helical chirality, for example, denoted A and A (or Pand Min the Cahn-Ingold-Prelog system). The formal condition for chirality is that the molecule should not have an improper axis of rotation (i.e. a rotation + reflection axis, 5n =... 

In spite of the high asymmetric induction observed in the Mo-catalyzed ARCM of 1,6-dienes, when 4a and 4b are used in reactions involving 1,7-dienes, inferior asymmetric induction is obtained. For example, as illustrated in Scheme 2, dienes 12 and 13 are not resolved with useful selectivity (krei < 5) when 4a is employed as the catalyst. To address this shortcoming, we took advantage of the modular character of the Mo complexes and prepared a range of chiral complexes as potentially effective catalysts. Accordingly, as depicted in Scheme 2, we... 

Attempts to achieve absolute stereocontrol by means of chiral sensitizers or chiral complexing agents [46] have seen little success with cyclohexenones and other unfunctionalized enone substrates. Ester 26, for example, underwent an... 

Transition metal containing chiral complexes exhibit some peculiar VCD behaviors which have fascinated researchers in inorganic chemistry and in spectroscopy. For example, an order of magnitude increase in the VCD intensity, with changes in sign for many VCD transitions, were detected for the open-shell sparteine complexes of Co(II) and Ni(II) as compared to the corresponding closed-shell Zn(II) complex... 

Organoaluminum compounds are heavily used in organic synthesis and the pertinent literature is too extensive to be adequately reviewed here. Readers are directed to excellent articles by Eisch for a general overview of the subject and are encouraged to search for specific transformations in the texts published by March and Larock. The text by Ojima cites several examples of enantioselective reactions using chiral complexes of aluminum. 

Asymmetric benzylic functionalization using a chiral base can be achieved. For example, reaction of complex (58) with the chiral base (59) and methyl iodide produce complex (60) in high yield and enantiomeric excess (Scheme 100). Asymmetric benzylic alkylation can also be obtained using the chiral complex (62) derived from enantioselective deprotonation of (61) (Scheme 101). High enantiomeric excess is observed upon deprotonation and alkylation of isobenzothiophen complexes with a chiral base (Scheme 102). 

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