Douglas Lloyd

Mndo study of bond orders in some conjugated BI- and tri-cyclic hydrocarbons

Abstract MNDO calculations have been carried out on a number of conjugated bicyclic and tricyclic hydrocarbons. For reference purposes some acenes and monocyclic non-benzenoid hydrocarbons are also mentioned. While the influence of 2 or 6 π-electron systems in stabilising, and of 4 π-electron systems in destabilising, structures is readily evident, it is clear that arrays of 10 or more π-electrons have markedly less effect, and the balance between fixation of bonds and delocalisation in many compounds possessing such systems is subtle.

Preparation and properties of some stable arsonium ylides

Abstract Stable crystalline arsonium ylides have been prepared by thermal decomposition of diazo compounds in the presence of triphenylarsine, and by condensation reactions of reactive methylene compounds with triphenylarsine oxide. The spectra of these ylides, and their reactions with benzaldehydes are discussed. Like other stabilised arsonium ylides they give alkenes rather than epoxides in Wittig reactions. They are generally more polar than their phosphonium analogues and also are more reactive in the Wittig reaction. With diphenylcyclopropenone some more reactive arsonium ylides form α-pyrones.

What Is Aromaticity

A brief review of the phenomenon of aromaticity is provided. The historical aspects of this property of molecules are covered, and contemporary views of aromaticity are described.

The effects of different copper (and some other) catalysts on the conversion of triphenyl- and tetraphenyl- diazocyclopentadienes and of some phenyliodonium αα′-dicarbonylylides into arsonium and other ylides

Abstract Diazo-compounds or iodonium ylides may be converted into arsonium and other ylides when heated in solution with triphenylarsine or other suitable carbene (or carbenoid) acceptor, and with a suitable Cu derivative present. The effects of using different copper complexes and salts are described and discussed. Other metal derivatives were for the most part ineffective as catalysts.

A stable and long-lived germaimine

Abstract Spectroscopic identification of the first reported stable germaimine is provided, together with an analysis of its bond structure; it exists in cisoid and transoid forms.

Effect of the counter-ion on the structures of tetraphenylantimony(V)–stibonium compounds: crystal and molecular structures of tetraphenylantimony(V) bromide, perchlorate, and tetraphenylborate

Crystals of Ph4SbBr are monoclinic, a= 16.293(3), b= 10.616(3), c= 12.507(2)A, β= 105.60(1)°, space group P21/n. The structure consists of trigonal bipyramidal molecules in which the apical Sb–Br bond is very long [2.965(1)A]: the apical and mean equatorial Sb–C distances are 2.151(9) and 2.102(9)A, respectively. The perchlorate [tetragonal, a= 12.670(2), c= 6.711(2)A, space group /] crystallises with isolated ions of almost perfect tetrahedral local symmetry; in the cation, the Sb–C distance is 2.095(2)A. The structures of a range of tetraphenylantimony(V) derivatives Ph4SbX are discussed in terms of the basicity/nucleophilicity of X. Crystals of Ph4SbBPh4 are tetragonal, a= 16.272(3), c= 13.703(3)A, with an I lattice: structure solution was attempted, without success, in all possible space groups. The SbPh4+ and BPh4– ions are scrambled.

1,5-Benzodiazepines

Publisher Summary This chapter discusses 1,5-Benzodiazepines. 1,5-Benzodiazepines are the 2,3-benzo-fused derivatives of the dihydrodiazepines. An alternative approach to the synthesis of benzodiazepines involves the reaction of β-chlorovinyl carbonyl compounds with o-phenylenediamine. In the first example methyl β-chlorovinyl ketone is used to obtain 5-methylbenzodiazepinium chloride. An extensive investigation has been made of the use of β-chlorovinylaldehydes for the preparation of 2,3-substituted benzodiazepines. Benzodiazepines and naphthodiazepines have also been prepared by addition and condensation of o-phenylenediamine, N-methyl-and N-phenyl-o-phenylenediamines, and 2,3-diaminonaphthalene with α-alkynyl ketones. Although the methylene signals of benzodiazepine bases appear as singlets at normal operating temperatures, at lower temperatures they give rise to double doublets. The results demonstrate that the benzodiazepine molecules take up boat conformations, which are, however, rapidly inverting at room temperature. Benzodiazepines and benzodiazepinium salts undergo ring contraction to give benzimidazoles when heated in aqueous solution. This presumably proceeds via ring-opening of the seven-membered ring to form a monoanil, with subsequent hydrolysis and ring closure to form a five-membered ring.

The preparation of some pyridinium cyclopentadienylides

Abstract The preparation of some pyridinium cyclo pentadienylides is described. A brief survey of earlier work in this field is included.

1,5-BENZODIAZEPINES AND 1,5-BENZODIAZEPINIUM SALTS

Publisher Summary This chapter discusses the formation, preparation, structure, and reactions of benzodiazepines and benzodiazepinium salts. It provides the treatment of 1,5- benzodiazepines that usually occur in the di-imine form. The protonation of benzodiazepines leads to the formation of monocations and dications. The most common method of preparation of 1,5-benzodiazepines is the reaction of o -phenylenediamine with 1,3-dicarbonyl compounds. The formation and preparation of benzodiazepines and benzodiazepinium salts take place from: 1,3–dicarbonyl compounds, β-chlorovinyl carbonyl compounds, α-alkynyl ketones, and sundry methods. Benzodiazepines have been prepared from perfluoro-enones in situ. There is no energetic driving force toward the formation of 1,5-benzodiazepines, with the lack of any marked stabilization of the 7-membered ring in the benzodiazepines. Benzodiazepines and benzodiazepinium salts undergo ring contraction to give benzimidazoles when heated in aqueous solution. In the formation of a benzimidazole, the steps involving the loss of a methyl ketone, which are essentially irreversible, control the course of the reaction. The reactions with electrophiles lead to the formation of acylation, alkylation, and deuteriation. The preparation of 2(4)-amino- and 2(4)-thio-benzodiazepines is also discussed in the chapter, because they show physiological and pharmacological activity.

2,3-Dihydro-1,4-diazepines

Publisher Summary This chapter discusses 2,3-dihydro-1,4-diazepines. The first diazepine to be prepared, namely the 5,7-dimethyl derivative, is obtained by condensation of acetylacetone with ethylenediamine, and the reaction between β-dicarbonyl compounds and 1,2-diamines has remained the commonest method for the preparation of these compounds. Dihydrodiazepines are extremely stable compounds over a very wide range of pH and their hydrolysis may be ignored at high alkalinity. Bisoxoenamines, on the other hand, are readily hydrolyzed and at all but moderately alkaline pH the hydrolysis equilibrium is such that this condensation is effectively suppressed, leaving formation of the dihydrodiazepine to proceed without competition. At moderately alkaline pH, however, the bisoxoenamine is stable and furthermore precipitates from solution. Thus, its formation competes successfully with the alternative reaction and it is the predominant product. At higher temperatures the yields of bisoxoenamine drop sharply even at the most favored pH values. Almost identical results are found in reactions of other alicyclic or aliphatic diamines with acetyl-acetone.