Carbonylation alkylative

J)-Alkyl(carbonyl)(i 5-cyclopentadienyl)(triphenylphosphane)irons (- )-(/ )-13 General Procedure18 ... 

Belonging to group (i) are alkylmetal carbonyls and cyclopentadienylmetal alkyl carbonyls of formula RMn(CO)5, CpFe(CO)2R, and CpMo(CO)3R. Solvent dependence of the reaction of MeMn(CO)5 with CjHi,NH2 is illustrated also in Table I. The rate varies markedly with the dielectric constant and with the nucleophilic power of the solvent. For example, on going from dimethylformamide to mesitylene, the rate of insertion is reduced by 10. Similarly, the sequence MeCN > MejCO > THF > CHCI3 > CjHj was reported for the reaction of MeMn(CO)5 with P(0CH2)3CR (R = Me and Et) in various solvents (97). Analogous trends were observed for the insertion reactions of CpFe(CO)2R and CpMo(CO)3R (48, 80, 98). 

Few quantitative data are available on the relative nucleophilicities of L toward various alkyl carbonyls. The rates of the reaction of CpMo(CO)3Me with L in toluene (Table II) decrease as a function of the latter reactant P( -Bu)3 > P( -OBu)j > PPhj > P(OPh)j, but the spread is relatively small (<8). The above order is that customarily observed for 8 2 reactions of low-valent transition metal complexes (J, 214). Interestingly, neither CpMo(CO)3Me nor CpFe(CO)2Me reacts with 1 or N, S, and As donor ligands 28, 79). This is in direct contrast to the insertion reactions of MeMn(CO)5 which manifest much less selectivity toward various L (see Section VI,B,C,D for details). 

No comparative kinetic study has been made on the same alkyl carbonyl system for two members of a given transition metal triad. Qualitative data show that the middle member is more reactive than the heaviest one e.g., CpMo(CO)jR > CpW(CO)jR (Section VI,B), Rh(III) > Ir(III) (Section VI,E), and Pd(II) > Pt(II) (Section VI,F). However, the extreme unreactivity of CpW(CO)jR and a considerable difference in lability between most alkyls of Rh(III) and Ir(III), as well as those of Pd(II) and Pt(II), have prevented detailed investigations. Surprisingly, no kinetic studies have been conducted on insertion reactions of RRe(CO)5, which would seem readily amenable to such investigations. 

Within group (i), square-planar EtPt(CO)(AsPh3)Cl inserts more rapidly than six-coordinate EtIr(CO)2(AsPh3)Cl2. In THE at 40°C, the relative k s are 9 and 1. Comparison of group (ii) alkyl carbonyls reveals the order MeMn(CO)5 > CpMo(CO)3Me > CpFe(CO)2Me. The ratios of the k s are 23 I and 100 1, respectively, in THF at 25° and 50.7°C. The higher reactivity of manganese than of molybdenum is a consequence of the relative entropies, whereas the lowest reactivity of iron is caused by its Jff (Table III). 

This same concept applies to spiroannulations of six membered rings and is illustrated in a synthesis of acorenone B 155 as outlined in Scheme 547). The notion of alkylative carbonyl transposition permits the spiro enone 156 to become a logical intermediate. The standard analysis by a retro-aldol process translates the spiro ring system of acorenone B into a geminal alkylation problem as revealed by... 

D-Glucono-1,5-lactone has been transformed (23) into trihydroxycarbox-ylates bearing a long-chain alkyl acetal group (15a,b). The synthesis involves the acetalation of HO-4 and HO-6 with a long-chain alkyl carbonyl com-... 

Other methods for preparing acyl complexes include the acylation of metallates and the treatment of alkyl carbonyl complexes with nucleophiles. 

In this context, an elegant alkylative carbonylation of alkenes accompanied by phenylselenyl transfer is described by Ryu and Sonoda. This three-component coupling involves the addition of a methoxycarbonylmethyl radical to an alkene, the trapping of the produced alkyl free radical by CO, and termination of the reaction by phenylselenenyl group transfer from the starting material. Yields are... 

On the basis of the CO dependence of the transformation of the P-chelates into the carbonyl acyl compounds, it was proposed that the rate-limiting step in the overall conversion of the P-chelates to carbonyl acyl complexes is related to the opening of the metallacycle by CO (steps a and b in Scheme 7.13) rather than to the following migratory insertion of the alkyl carbonyl complex that is independent of the CO pressure (step c). 

Excellent enantioselectivities up to complete asymmetric induction are achieved in the preparation of a-alkylated aldehydes, acyclic and cyclic ketones via (-)-(S)- and (+ )-(7 )-1 -amino-2-methoxymethylpyrrolidine (SAMP/RAMP-hydrazones) (see Section 1.1.1.4.2.). Due to the unique mechanism of metalation and alkylation, the absolute configuration of the final products can be predicted. Since both antipodes of the auxiliary are available, either enantiomer of the desired alkylated carbonyl compound can be prepared... 

The metalated hydrazones are alkylated by alkyl halides, dialkyl sulfates or alkyl sulfonates at low temperatures in tetrahydrofuran (—95°C) or diethyl ether (— 110°C) to form the a-sub-stituted hydrazones in nearly quantitative yields. The ambident azaenolates react exclusively at the C-terminus side products resulting from N-, di-, or polyalkylation are not observed. The crude alkylated hydrazones can be purified by distillation or silica gel chromatography (diethyl ether/pentane) without epimerization. However, in most cases, they are pure enough to be directly cleaved to the desired alkylated carbonyl compound. 

Alkylated Carbonyl Compounds and Recovery of the Chiral Auxiliary by Cleavage of Alkylated SAMP/ RAMP-Hydraznnes General Procedure for Ozonolysis3 ... 

Alkylated Carbonyl Compounds by Cleavage of Alkylated SAMP/RAMP-Hydrazoncs General Procedure for Acidic Hydrolysis of Methoiodides ( Salt Method )3 ... 

Since the above cleavage methods proceed without racemization, the enantiomeric excess of the alkylated carbonyl compounds obtained can be safely determined by measuring the diastereomer-ic ratio of the alkylated hydrazones (see Section I.I.I.4.2.3.). The diastereomeric excess of SAMP-hydrazones derived from aldehydes was further determined by gas chromatography41. 

In late 1975, Enders et al.156) started a research project directed towards the development of a new synthetic method for asymmetric carbon-carbon bond formation. A new chiral auxiliary, namely the (S)-proline derivative SAMP (137), was allowed to react with aldehydes and ketones to give the hydrazones (138), which can be alkylated in the a-position in an diastereoselective manner 157,158). Lithiation 159) of the SAMP hydrazones (138), which are formed in excellent yields, leads to chelate complexes of known configuration 160). Upon treatment of the chelate complexes with alkyl halogenides the new hydrazones (139) are formed. Cleavage of the product hydrazones (139) leads to 2-alkylated carbonyl compounds (140). 

Alkyl carbonyl complexes can create vacant coordination sites by alkyl migration to give acyls far more readily than hydride carbonyl complexes can... 

The above conclusions and suggestions, if valid, require than an alkyl carbonyl (because it can easily generate a vacant coordination site) and a hydride should be able to carry out a facile dinuclear alkane elimination. Thus we predict that dinuclear eliminations between Os(CO)4H2 and Os(CO)4(CH3)2 should occur more rapidly than the decomposition of either compound separately, and we have confirmed this prediction. 

Unlike manganese, rhenium is reported to form an alkyl compound, dimethyl rhenium. Re(CH )3. Like manganese, it forms a dirhenium compound with carbon monoxide, (CO)5ReRe(CO)5, as well as hydrogen-halogen and alkyl-carbonyl compounds. It also forms a dicyclopentadienyl compound, (CsHjJReH. 

The fact that there is such a paucity of metal formyl complexes is both interesting and significant because of the proposed intermediacy of coordinated formyl in CO reduction, and the sharply contrasting abundance of metal acyl complexes. Since many of the acyl complexes are known to form by migratory insertion of CO in an alkyl carbonyl complex (20, 20a, 22), the lack of formyl complexes from hydride carbonyls relates to the thermodynamic difference in the equilibrium (5) when Y is alkyl and when it is hydride. 

Finally, a comparison of the behavior of the three alkyl carbonyl complexes 7)5-C5H5Mo(CO)3Me (722), i75-C5H5Fe(CO)2Me (123), and C3F7Fe(CO)3(PPh3)I (124) toward liquid NH3 shows completely different reaction character. 

R1=aryl, alkyl, carbonyl, ether, alcohol R2=H, alkyl, acetate, ether, OH X=0, N, C(C02IVle)2... 

After Cram had discovered the selectivities now named after him, he proposed the transition state model for the formation of Cram chelate products that is still valid today. However, his explanation for the preferred formation of Cram products was different from current views. Cram assumed that the transition state for the addition of nucleophiles to a-alkylated carbonyl compounds was so early that he could model it with the carbonyl compound alone. His reasoning was that the preferred conformation of the free a-chiral carbonyl compound defines two sterically differently encumbered half-spaces on both sides of the plane of the C=0 double bond. The nucleophile was believed to approach from the less hindered half-space. 

Ryu, I., Muraoka, H., Kambe, N., Komatsu, M., and Sonoda, N. (1996) Group transfer carbonylations photoinduced alkylative carbonylation of alkenes accompanied by phenylselenenyl transfer. Journal of Organic Chemistry, 61, 6396-6403. 

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