Ab initio SCF computations have been performed on allyllithium using STO/3G atomic orbitals. Both the covalent and the ion-pair structures have been investigated and their energies minimized with respect to most of the geometrical parameters. The ion-pair structure is found to be more stable by 8 kcal/mol and a simple bonding scheme leads to the interpretation of its stability.

SCF energies have been obtained for various geometries of pentadienyllithium using STO/3G atomic orbitals. In agreement with experiment, the “W”-form of the pentadienyl anion is shown to be the most stable. For the covalent molecule, the strong chelating ability of the lithium atom favours a non planar structure.

AbstractBei der Reaktion geminaler Dibromide in THF mit Carbonylverbindungen, wie z.B. (I), in Gegenwart von Li/THF bei 25°C oder von Butyl‐Li in Hexan bei ‐78°C entstehen primär α‐Brom‐Li‐Derivate, wie z.B. (II), die sich mit (II) zu Oxiranen vom Typ (III) (35‐95% Ausbeute) umsetzen.

A general oxirane synthesis from a geminal dibromide and a carbonyl compound was studied. The reaction proceeds through an α-bromolithium species, most conveniently generated by reacting a geminal dihalogenide (e.g. ethylidene, isopropylidene, benzylidene bromide and ethyl dibromoacetate) and butyllitium or lithium suspended in THF. Aliphatic, alicyclic and aromatic aldehydes and ketones give rise to the corresponding epoxides, in good yields.

AbstractDie Carbonylverbindungen (I) reagieren mit in situ erzeugtem CH2LiBr (aus CH2Br2 (II) und Li, LiHg oder n‐Butyl‐Li in der Kälte) in THF zu den Oxiranen (III) (Ausbeuten 35‐52%).

The reaction between bromolithiummethane and carbonyl compounds has been studied. The organometallic species has been generated in situ by reacting dibromomethane and butyllithium, lithium suspension or amalgam in THF. Aliphatic, alicyclic and aromatic aldehydes and ketones give rise to the corresponding epoxides generally in satisfactory yields, α,β-unsaturated carbonyl compounds do not react under the mentioned conditions and this is useful if selectivity is required. The influence of the solvent on the reaction course is also discussed.

The reaction between bromolithiummethane and carbonyl compounds has been studied. The organometallic species has been generated in situ by reacting dibromomethane and butyllithium, lithium suspension or amalgam in THF. Aliphatic, alicyclic and aromatic aldehydes and ketones give rise to the corresponding epoxides generally in satisfactory yields, α,β-unsaturated carbonyl compounds do not react under the mentioned conditions and this is useful if selectivity is required. The influence of the solvent on the reaction course is also discussed.

The reaction of 1,1-dihalo-alkanes with magnesium and magnesium amalgam has been studied. Methylene bromide and iodide yield, under suitable conditions, a stable solution of methylene magnesium halide which easily olefinates aldehydes and ketones affording the corresponding methylenic olefins in good yields. Other alkylidene halides, under the conditions studied, do not give any stable geminal dimagnesium compound although geminal species are probably present during the in situ reaction between alkylidene halides, carbonyl compounds and magnesium amalgam. A general carbonyl olefination scheme taking into account the majority of the known reactions of this kind is proposed.

AbstractDie Reaktion der Dihalogenide (I) mit Mg oder Mg/Hg in Äther führt zu den stabilen Mg‐halogeniden (II), die mit Aldehyden und Ketonen, z.B. (III), die Olefine (IV) (Ausbeuten 40‐70%) bilden.

The reaction of 1,1-dihalo-alkanes with magnesium and magnesium amalgam has been studied. Methylene bromide and iodide yield, under suitable conditions, a stable solution of methylene magnesium halide which easily olefinates aldehydes and ketones affording the corresponding methylenic olefins in good yields. Other alkylidene halides, under the conditions studied, do not give any stable geminal dimagnesium compound although geminal species are probably present during the in situ reaction between alkylidene halides, carbonyl compounds and magnesium amalgam. A general carbonyl olefination scheme taking into account the majority of the known reactions of this kind is proposed.

Chemischer Informationsdienst. Organische ChemieVolume 1, Issue 17 Preparative Organic Chemistry ChemInform Abstract: ALKENE AUS EPOXIDEN DURCH REDUKTIVE ELIMINIERUNG MIT MAGNESIUMBROMID UND MAGNESIUMAMALGAM F. BERTINI, F. BERTINISearch for more papers by this authorP. GRASSELLI, P. GRASSELLISearch for more papers by this authorG. ZUBIANI, G. ZUBIANISearch for more papers by this authorG. CAINELLI, G. CAINELLISearch for more papers by this author F. BERTINI, F. BERTINISearch for more papers by this authorP. GRASSELLI, P. GRASSELLISearch for more papers by this authorG. ZUBIANI, G. ZUBIANISearch for more papers by this authorG. CAINELLI, G. CAINELLISearch for more papers by this author First published: April 28, 1970 https://doi.org/10.1002/chin.197017171Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume1, Issue17April 28, 1970 RelatedInformation

Oxirans may be obtained by treating carbonyl compounds in tetrahydrofuran with methylene bromide and lithium or lithium amalgam.

The straightforward synthesis of polycarbosilanes (PCS) was achieved via the polycondensation of chlorosilanes and chloromethanes using magnesium (Mg) and titanium(IV) tetrachloride (TiCl4). In this polycondensation, TiCl4 acts as an efficient catalyst and the combined use of Mg and TiCl4 is necessary to produce PCS. The resulting PCS are viscous colored oils that are soluble in organic solvents. The number-average molar mass (Mn; 1.0–1.5 kg mol−1) and molar-mass dispersity (ÐM; 1.3–1.9) values of the resulting PCS were determined by size-exclusion chromatography (SEC) using polystyrene standards. The 1H, 13C{1H}, and 29Si{1H} NMR as well as IR spectra of the resulting PCS revealed that they consist of Si–C, Si–H, Si(H)–H, C–C, and Si–Si bonds. The structures of the resulting PCS vary depending on the structures of the monomers and their initial molar ratios. The ceramic yields from the obtained PCS (23–70%) depend on the original structures of the PCS. A plausible mechanism of this polycondensation is proposed based on the results of polycondensations and model reactions.

Trisporic-C acid is the major component of a biologically active acidic fraction isolated from submerged cultures of Choanephora trispora. On the basis of the chemical and spectrochemical data and synthesis, structure I′—a monocyclic trienic hydroxyketo acid—has been assigned to the product. Trisporic-B acid differs from the C acid by the absence of an alcoholic hydroxyl group.

Using ab initio electronic structure methods with flexible basis sets, we examined the electronic, geometric, and thermodynamic stability of selected borata-alkene synthons (H2C = BR2)– (R = H, CH3, C6H5, C6F5, Mes). The isolated (H2C = BH2)– synthon was found to be electronically stable and susceptible to neither fragmentation nor isomerization processes. Geometric and electronic stabilities of the remaining (H2C = BR2)– anions were confirmed likewise. The structures of borata-alkene synthons studied contain planar H2C = B < fragment with the apparent double-bond character of the C–B connection confirmed by natural bond orbital occupancies of σ(C–B) and π(C–B) bonds approaching 2 e and by the shapes and spatial localizations of the corresponding NBOs. Vertical electron detachment energies (1.70–3.29 eV) of the (H2C = BR2)– synthons were predicted and compared to those of the representative alkenyl carbanions. The stability and structures of sodium salts comprising the (H2C = BR2)– unit and their ability to preserve the basic properties of the borata-alkene synthons were determined and discussed.

α‐Monoboryl anions show remarkable stability due to the valence deficiency of the adjacent three‐coordinate boron center and can be expressed as its resonance form, the borata‐alkene systems [R2B=CH2]−. The diversity of synthetic approaches as well as the properties of the C=B bond are disclosed in this review, dealing with both electronic and structural properties of the boryl moieties involved. Full characterization in solid state by X‐ray diffraction demonstrated the short distances between B and C, as a consequence of the boron ylide character in the boron‐stabilized carbanions. This review includes a collection of C−B length distances as well as 11B NMR data that can be useful for diagnostic evidence of the partial boron‐carbon double‐bond character. Natural bond orbital (NBO) analysis on DFT computed structures also supports and justifies the borata‐alkene character.The reactivity of the C=B bond acting as nucleophilic synthon is unveiled through extensive electrophilic trapping examples. The homologation protocols with diborylmethane, via single carbon chain extension, involves a facile introduction of the C(sp3)−B bonds, which can be subsequently transformed into functionalized target products, containing C−O, C−N or C−C bonds.

A new approach to androsterone and 19-norandrosterone from androst-5-ene-3β-ol-17-one and 19-nortestosterone is described. The synthesis is accomplished by a stereospecific hydroboration of Δ 3 - 5α-steroids.