Organometallic Compounds Substitution

Prior to the development of methods for caiTving out the direct reaction of fomialdehyde vdth acetydene or monosubstituted acetylenes (page 237), the only satisfactory procedime for preparing acetylenic alcohols from formaldehyde involved the intennediate preparation of organometallic compounds. Substituted pi Opargyl alcohols are obtained in yields of 70 per cent or better by reaction of monosubstituted acetylenic Grignard compounds with gaseous formaldehyde ... 

Organometallic compounds are named as substituted derivatives of metals The metal is the parent and the attached alkyl groups are identified by the appropriate prefix... 

Another such effect is the intervention of cyclic transition states in reactions of organometallic compounds (Section II, B, 5) with azines or in intramolecular nucleophilic substitutions (Section II, F). 

Mechanistically the reaction can be divided into two steps. Initially the alkyl halide 1 reacts with sodium to give an organometallic species 3, that can be isolated in many cases. In a second step the carbanionic R of the organometallic compound 3 acts as nucleophile in a substitution reaction with alkyl halide 1 to replace the halide ... 

Additions of organometallic compounds to 2-azelidinones such as 1 or 4 bearing a leaving group in the 4-position preferentially or exclusively afford tram-3,4-substituted /(-lactams 3 or 6. Therefore, the participation of an A -acylinline intermediate such as 2 or 5 which is attacked from the less hindered side is probable14-16. This has been exploited for the synthesis of carbapenem antibiotics, e.g., thienamycin (7)16. 

Reutov, O. A., The mechanisms of the substitution reactions of non-transition metal organometallic compounds, J. Organomet. Chem. 100, 219 (1975). 

Keto Derivatives of Group IV Organometalloids, 7, 95 Lewis Base-Metal Carbonyl Complexes, 3, 181 Ligand Substitution in Transition Metal ir-Complexes, 10, 347 Literature of Organo-Transition Metal Chemistry 1950-1970, 10, 273 Literature of Organo-Transition Metal Chemistry 1971,11, 447 Literature of Organo-Transition Metal Chemistry 1972, 12, 379 Mass Spectra of Metallocenes and Related Compounds, 8, 211 Mass Spectra of Organometallic Compounds, 6, 273... 

In some reactions of carbanions or organometallic compounds with very weak acids the base has a choice of protons and can give more than one salt. An example is the nuclear metallation of a substituted benzene in which the product may be oriented ortho, meta, or para. The actual results of a few such reactions are shown in Table XII. 

One equivalent of LiHBEt3 or LiHB(sec-butyl)3 in THF at -80° consumed the phosphine substituted a,8-dialkoxyethylidene salts 9a, b and delivered 73% yields of the formylmethyl complex CpFe(CO)PPh3(CH2CHO) (21) as the only isolable organometallic compound. The product 21 can be accounted for by an electrophile... 

Vinylidene complexes are valuable intermediates for the preparation of heteroatom-substituted earbene eomplexes (Seetion 2.1.5) and other organometallic compounds, including non-heteroatom-substituted earbene eomplexes [573,574]. Examples of further transformations of vinylidene complexes include addition reac-... 

Non-heteroatom-substituted carbene complexes play a key role both as reagents and catalysts in organic synthesis and as intermediates in the preparation of other organometallic compounds. However, discussion of applications in inorganic synthesis would surpass the scope of this book. Here the focus will be on those reactions which lead to metal-free compounds and hence are particularly relevant to the organic chemist. 

The polarity of carbon-halogen bond of alkyl halides is responsible for their nucleophilic substitution, elimination and their reaction with metal atoms to form organometallic compounds. Nucleophilic substitution reactions are categorised into and on the basis of their kinetic properties. Chirality has a profound role in understanding the reaction mechanisms of Sj l and Sj 2 reactions. Sj 2 reactions of chiral all l halides are characterised by the inversion of configuration while Sj l reactions are characterised by racemisation. 

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