Carbon monoxide chirality

Alkylation of the anion 2 with iodomethane or other haloalkanes provides alkyldicarbonyl(t/5-cyclopentadienyl)iron complexes such as 53,0 (see also Houben-Weyl, Vol. 13/9a, p 209). Migratory insertion of carbon monoxide occurs on treatment with phosphanes or phosphites9 -11 (see also Houben-Weyl, Vol. d3/9a, p257) to provide chiral iron-acyl complexes such as 6. This is the most commonly used preparation of racemic chiral iron-acyl complexes. 

The reported preparations of enantiomerically pure chiral iron-acyl complexes have relied upon resolutions of diastereomers. One route1415 (see also Houben-Weyl, Vol. 13/9 a, p 421) employs a resolution of the diastereomeric acylmenlhyloxy complexes (Fe/ )-3 and (FeS )-3 prepared via nucleophilic attack of the chiral menlhyloxide ion of 2 at a carbon monoxide of the iron cation of 1. Subsequent nucleophilic displacement of menthyloxide occurs with inversion at iron to generate the enantiomerically pure iron-acyl complexes (i>)-4 and (f )-4. 

Subsequent carbonylation of the alkyl-iron complexes with carbon monoxide provides the desired chiral iron-acyl complexes, with essentially complete inversion of configuration at... 

The dicarbonyl species thus produced undergo photolytically promoted carbon monoxide displacement by phosphine to give racemic mixtures of chiral a,/ -unsaturated iron-acyl complexes35. 

Borane, 1-methylbenzylaminocyanohydropyrrolyl-, 3, 84 Borane, thiocyanato-halogenohydro-, 3,88 Borane, trialkoxy-amine complexes, 3, 88 Borane, triaryl-guanidine complexes, 2,283 Borane, trifluoro-complexes Lewis acids, 3,87 van der Waals complexes, 3, 84 Borane complexes aminecarboxy-, 3,84 aminehalogeno-, 3, 84 amines, 3, 82, 101 B-N bond polarity, 3, 82 preparation, 3, 83 reactions, 3, 83 bonds B-N, 3, 88 B-O, 3, 88 B-S, 3, 88 Jt bonds, 3, 82 carbon monoxide, 3, 84 chiral boron, 3, 84 dimethyl sulfide, 3, 84 enthalpy of dissociation, 3, 82... 

The intramolecular cyclization of l,2-dien-7-ynes and l,2-dien-6-ynes regiospecifically affords the corresponding titanacycles, which react with protons, carbon monoxide, aldehydes, or imines to give single products, as shown in Eqs. 9.56 and 9.57 [102], As the formation of titanacycles and their subsequent reaction with externally added reagents such as carbon monoxide (Eq. 9.56) or an aldehyde (or imine) (Eq. 9.57) proceeds with excellent chirality transfer, this represents a new method for synthesizing optically active cyclopentane derivatives from optically active allenes [102]. 

An Rh-catalyzed asymmetric [4 +l]-cycloaddition of vinylallenes with carbon monoxide was realized for the first time to furnish chiral 5-substituted 2-alkylidene-3-cydopentenones (Scheme 16.42) [42],... 

By contrast, in 2000 Shibata reported the Ir-catalyzed enantioselective Pauson-Khand-type reaction of enynes [30aj. The chiral Ir catalyst was readily prepared in situ from [lrCl(cod)]2 and tolBINAP (2,2 -bis(di-p-tolylphosphino)-l,T-binaphthyl), both of which are commercially available and air-stable, and the reaction proceeded under an atmospheric pressure of carbon monoxide. The Ir-catalyzed carbonylative coupling had a wide generality in enynes with various tethers (Z), substituents on the alkyne terminus (R ) and the olefinic moiety (R ). In the case of less-reactive enynes, a lower partial pressure of carbon monoxide achieved a higher yield and ee-value (Table 11.1) [30b]. 

A similar carbonylative coupling reaction was applied to the kinetic resolution of secondary alcohols [63]. In the presence of a Pd catalyst ligated by chiral oxazolinylferrocenylphosphine, the pentavalent Ph3Bi(OAc)2 and carbon monoxide effectively benzoylated secondary alcohols, and up to 48% enantiomeric excess (ee) was attained (Scheme 47). Although the enantioselectivity is not satisfactory, this is a unique new procedure for the kinetic resolution. 

Bis(oxazoline) ligands have also been used to produce polymers containing main chain chirality. Some examples include those by Wagner and co-workers in which /-pr-box 45 is used to mediate the copolymerization of tert-butylstyrene 192 with carbon monoxide to achieve a polymer of type 193 with stereoregularity up to 98%, ° ° Oishi and co-workers polymerization of A-substimted maleimides... 

Substitution of a carbon monoxide ligand of complexes, such as 1, by the more electron-donating triphenylphosphane group (see Section 1.1.1.3.4.1.3.) provides chiral monophos-phane complexes, such as 3. Monophosphane complexes in general lack sufficient electrophilic-ity to react with amines or thiols, but react readily with amine anions at the /J-position, producing enolate anions such as 4, which may be quenched stereoselectively at the a-carbon by electrophiles46 (see Section 1.1.1.3.4.1.3.). The conformational and stereochemical issues involved are essentially identical to those already discussed in this section for the 1,4-additions of carbon nucleophiles. 

In fact, this approach constituted one of the earliest trials. One is introduction of a chiral ligand like glyphos on cobalt by replacing one of the carbon monoxides to obtain an enantiomerically enriched new metal-alkyne complex. The second approach is use of the propargyl alcohol bearing a chiral auxiliary. Replacement of only one carbon monoxide would lead to a mixture of diastereomers. In both cases, a I I mixture of products was obtained, and each diastereomer was separated before the... 

The prevailing chirality of the aldehyde produced using ( — )-DIOP as the asymmetric ligand is [ (R) ] for vinyl olefins where the asymmetric carbon atom arises from the attack of carbon monoxide at the carbon atom in position 2. The same chirality [ (R) ] is found also for vinylidene olefins where the asymmetric carbon atom arises from the attack of a hydrogen atom on the same carbon atom. 

Cis- and trans-butene under similar conditions yield 2-methylbutanal with prevailing [ (S) ] chirality. The same [ (S) ] prevailing chirality was found in the case of cis- and trans-2-hexene for the aldehydes arising from the attack of carbon monoxide at the carbon atom in position 2, accounting for 60% of the aldehydes formed. The opposite chirality... 

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