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Functional derivatives of gem-dibromocyclopropanes (ethers and esters of gemdibromocyclopropylmethanol, 2,2-dibromocyclopropanecarboxylic acids and their esters) undergo partial hydrodebromination at the treatment with isopropyl magnesium bromide (3–6 mol-equiv) in THF and then in methanol at −60°C affording the corresponding monobromides in 64–95% yields. The addition of nonsolvated magnesium bromide to the reaction mixture results in the considerable reduction of the amount of the Grignard reagent (from 6 to 3 mol-equiv). This allows achieving the partial hydrodebromination of 2,2-dibromocyclopropanecarboxylic acids.

1-Trimethylsilyl-3-phenylcyclopropene undergoes a highly stereocontrolled ene-reaction to give a dimer and further reaction leads to one or more trimers derived through two ene-reactions.

A convenient and inexpensive approach to the generation of 3-phenylcyclopropenes is described. Reaction of these compounds with a range of dienophiles and dipolarophiles led to the stereoselective formation of [4+2]- and [3+2]-cycloadducts, which were exclusively exo -3-phenyl- cis -1,2-disubstituted cyclopropanes. Efficient trapping of 1-lithio-3-phenylcyclopropene with different electrophiles is also discussed. Ab initio calculations suggest that the lowest energy conformation of 3-phenylcyclopropene has the plane of the benzene ring perpendicular to the cyclopropene π-bond but with a low rotation barrier.

The effects of substitution of X=C by Si or Ge in X(CH3)3 moieties attached to the formal double bond of 3,3-dimethylcyclopropene are examined. Regularities in observed trends of vibrational frequencies implicating the moieties containing the X atom, as the X atomic mass is increased, are extrapolated to X=Sn. The results of this extrapolation made it possible to assign the known experimental vibrational frequencies of 3,3-dimethyl-1-(trimethylstannyl)cyclopropene and 3,3-dimethyl-1,2-bis(trimethylstannyl)cyclopropene.

Oxidation of gem -dibromocyclopropanes with chromium trioxide in acetic acid or a number of other reagents is generally slower than that of the corresponding cyclopropane; in a number of cases moderate yields of products are obtained but these show unexpected oxidation patterns.

This review surveys both data obtained by the authors and published data on the partial or full hydrodehalogenation of di- and polyhalocyclopropanes (chlorides and bromides) with Grignard reagents catalyzed by titanium or zirconium compounds. The factors affecting the efficiency and selectivity of the hydrodebromination of bromocyclopropanes are considered: the nature of Grignard reagents (including isotopically labeled reagents), their transformations and effects in catalyzed and uncatalyzed reactions, the participation of solvents, catalytic and stoichiometric amounts of the catalyst, etc. A scheme is proposed in which the key steps of the mechanism of hydrodebromination of bromocyclopropanes includes three blocks of reactions: (a) the generation of a catalytically active Ti(II) species; (b) the hydrodehalogenation of bromocyclopropanes involving electron transfer from a low-valent catalyst species, formation of the cyclopropyl radical, and stabilization of this radical as a result of hydrogen atom transfer from the solvent molecule; and (c) transformations of previously formed radical species, such as dimerization and disproportionation (for example, of radical species generated from Grignard reagents or ether molecules) or the linking of alkyl radicals to radical species produced from solvent molecules.

Reaction of gem -dibromocyclopropanes with ethylmagnesium bromide at ambient temperature leads to very high yields of allenes; when cyclopropylidene–allene ring opening is suppressed, alternative carbenic products are observed, although other reactions compete. When the reactions are carried out at −60°C, a 1-bromo-1-(bromomagnesio)-cyclopropane is formed which may be trapped by a number of electrophiles.

Reaction of 2-acylaminomethyl-1,1-dibromocyclopropanes with methyllithium at −90°C leads to selective bromine-lithium exchange and cyclisation to give a 1-bromo-3-azabicyclo[3.1.0]hexan-2-ol.

1,1-Dibromocyclopropanes are converted into the corresponding monobromocyclopropanes (as mixtures of stereoisomers where appropriate) by reaction with 1.0–1.3 mol equiv. of ethylmagnesium bromide and 2–10 mol% titanium isopropoxide for 90%). With ethylmagnesium bromide, the reaction occurs very slowly in the absence of catalyst; with methylmagnesium bromide, the reaction does occur in the absence of catalyst, but is only slightly promoted in the presence of titanium isopropoxide. Reactions with a number of other Grignard reagents are also discussed. In the case of phenethylmagnesium bromide, the major product containing the phenethyl-group is ethylbenzene, together with small amounts of styrene and ethyl 4-phenyl-2-butyl ether, a product of trapping of the solvent, ether. In other cases, relatively large amounts of a diether, formally derived by hydrogen abstraction adjacent to the ether oxygen followed by dimerisation, are isolated. No products were identified incorporating the cyclopropane and either the Grignard alkyl group or the solvent. Labelling studies indicate that the hydrogen introduced into the cyclopropane is not derived from either the α- or β-positions of the Grignard reagent. When the reduction is carried out with phenethylmagnesium bromide in d8-tetrahydrofuran both monobromides contain deuterium.

Simple chiral building blocks 1-(R)- and 1-(S)-2,2-dibromocyclopropanecarboxylic acids and 2-(R)-bromo-1-(S)-cyclopropanecarboxylic acids and their 1-methyl analogues, have been obtained on a preparatively useful laboratory scale.

Reaction of 2-acyloxymethyl or 2-acylaminomethyl-1,1-dibromocyclopropanes with methyllithium at −90°C leads to selective bromine-lithium exchange and intramolecular cyclisation to give a 1-bromo-3-oxa- or 1-bromo-3-aza-bicyclo[3.1.0]hexan-2-ol.

The molecular structure and conformation of 3-ethenyl-3-methyl-cyclopropene have been studied experimentally by the gas electron diffraction method. A conformational mixture consisting of 75.4(3.1)% anti (ω(C 3 C 4 ): 180°) and 24.6% gauche (ω(C 3 C 4 ): 52.2(4.6)°) was observed. Theoretical ab initio optimization calculations at the MP 2 6–31 G ∗ level have also been performed. They include a potential scan which showed two energy minima, one at ω(C 3 C 4 ) equal to 180° ( anti ) and the other at ω(C 3 C 4 ) equal to ± 20.3° ( gauche ). The calculated energy difference between the two minima was 1.03 kcal/mol, with anti as the lower minimum. This corresponds to a conformational composition of 73.3% anti and 26.7% gauche , in excellent agreement with the experimental results. The gauche → anti and anti → gauche potential barriers were calculated to be 2.3 and 3.4 kcal/mol, respectively.

Intramolecular insertion of single enantiomers of cyclopropylidenes into 5,6-related CH bonds adjacent to nitrogen has been used to obtain enantiomerically pure methanoproline and a number of analogues with a high degree of one- or two-fold asymmetric induction.

1,1-Dibromo- and 1,1-dichlorocyclopropanes are converted into the corresponding monohalo-cyclopropanes (as mixtures of stereoisomers where appropriate) by reaction with 1.2–1.3 mol. equiv. of ethyl magnesium bromide and a small amount of titanium isopropoxide in ether. In the presence of an excess of ethylmagnesium bromide the product from the dibromide is the non-halogenated cyclopropane.

Reactions of the methoxide ion with substituted halocyclopropanes, which result in E2 elimination, have been studied by the semiempirical quantum-chemical AM1 method. The transition states corresponding totrans andcis routes have been localized. The energetic predominance of thetrans route over thecis route is reduced by 2.6 kcal mol−1 on going from 1-chloropropane to chlorocyclopropane because of the features of cyclopropane geometry. It has been demonstrated that, in the gas phase,cis elimination may predominate overtrans elimination for a particular stereoisomer of 2-cyano-2-methyl-1-halocyclopropanes due to weakening of orbital interactions and Coulomb repulsion between the cyano group and the MeO− anion in thetrans E2 transition state.

1 Dehydrohalogenations of Halogenated Cyclopropanes 2 Elimination of Halogen 3 1,2-Elimination of a Trialkylsilylhalide 4 Eliminations Leading to Cyclopropa-Aromatics 5 1,1- and 1,3-Elimination Leading to Cyclopropenes 6 1,3-Dehalogenation of 1-Halo-2-Halomethylcyclopropanes 7 Eliminations Leading to Bicyclo[1.1.0]but-1(3)-enes 8 1,2- and 1,3-Eliminations in Quadricyclanes 9 Dehalogenation and Dehydrohalogenation of Halogenated Cyclopropenes Keywords: dehydrohalogenations of halogenated cyclopropanes; halogen elimination; eliminations involving carbon–halogen bonds; gas phase dehalogenations; dehalosilylation; gas phase elimination; bicyclopropene and spiropentadine preparation; eliminations leading to cyclopropa-aromatics

Intramolecular insertion of single enantiomers of cyclopropylidenes into 5,6-related CH bonds adjacent to nitrogen has been used to obtain enantiomerically pure methanoproline and a number of analogues with a high degree of one- or two-fold asymmetric induction.

Reaction of 2-acyloxymethyl or 2-acylaminomethyl-1,1-dibromocyclopropanes with methyllithium at −90°C leads to selective bromine-lithium exchange and intramolecular cyclisation to give a 1-bromo-3-oxa- or 1-bromo-3-aza-bicyclo[3.1.0]hexan-2-ol.

Simple chiral building blocks 1-(R)- and 1-(S)-2,2-dibromocyclopropanecarboxylic acids and 2-(R)-bromo-1-(S)-cyclopropanecarboxylic acids and their 1-methyl analogues, have been obtained on a preparatively useful laboratory scale.

Reaction of gem -dibromocyclopropanes with ethylmagnesium bromide at ambient temperature leads to very high yields of allenes; when cyclopropylidene–allene ring opening is suppressed, alternative carbenic products are observed, although other reactions compete. When the reactions are carried out at −60°C, a 1-bromo-1-(bromomagnesio)-cyclopropane is formed which may be trapped by a number of electrophiles.

1 Dehydrohalogenations of Halogenated Cyclopropanes 2 Elimination of Halogen 3 1,2-Elimination of a Trialkylsilylhalide 4 Eliminations Leading to Cyclopropa-Aromatics 5 1,1- and 1,3-Elimination Leading to Cyclopropenes 6 1,3-Dehalogenation of 1-Halo-2-Halomethylcyclopropanes 7 Eliminations Leading to Bicyclo[1.1.0]but-1(3)-enes 8 1,2- and 1,3-Eliminations in Quadricyclanes 9 Dehalogenation and Dehydrohalogenation of Halogenated Cyclopropenes Keywords: dehydrohalogenations of halogenated cyclopropanes; halogen elimination; eliminations involving carbon–halogen bonds; gas phase dehalogenations; dehalosilylation; gas phase elimination; bicyclopropene and spiropentadine preparation; eliminations leading to cyclopropa-aromatics

The ionization potentials (IP) of the 1-methyl-1-alkenylcyclopropanes and 3-methyl-3-alkenylcyclopropenes were measured by Photoelectron Spectroscopy (PES). The conformations of these molecules were calculated by MO (AM-1) method. It was concluded that orthogonal conformations (goch) are more characteristic in the series of alkenylcyclopropanes, meanwhile in the series of alkenylcyclopropenes symmetric forms (cis or trans) are more possible.

Selective methods for the preparation of 3-phenylcyclopropene and its 1-substituted derivatives are provided. The parent cyclo- propene is readily trapped in (3+2)- and (4+2)-cycloadditions that lead toexo-3-phenyl-1,2-disubstituted cyclopropanes.Ab initiocalculations suggest that the lowest energy conformation has the plane of the benzene ring perpendicular to the cyclopropeneπ-bond but with a low rotation barrier.

This review surveys both data obtained by the authors and published data on the partial or full hydrodehalogenation of di- and polyhalocyclopropanes (chlorides and bromides) with Grignard reagents catalyzed by titanium or zirconium compounds. The factors affecting the efficiency and selectivity of the hydrodebromination of bromocyclopropanes are considered: the nature of Grignard reagents (including isotopically labeled reagents), their transformations and effects in catalyzed and uncatalyzed reactions, the participation of solvents, catalytic and stoichiometric amounts of the catalyst, etc. A scheme is proposed in which the key steps of the mechanism of hydrodebromination of bromocyclopropanes includes three blocks of reactions: (a) the generation of a catalytically active Ti(II) species; (b) the hydrodehalogenation of bromocyclopropanes involving electron transfer from a low-valent catalyst species, formation of the cyclopropyl radical, and stabilization of this radical as a result of hydrogen atom transfer from the solvent molecule; and (c) transformations of previously formed radical species, such as dimerization and disproportionation (for example, of radical species generated from Grignard reagents or ether molecules) or the linking of alkyl radicals to radical species produced from solvent molecules.

The effects of substitution of X = C by Si or Ge in X(CH(3))(3) moieties attached to the formal double bond of 3,3-dimethylcyclopropene are examined. Regularities in observed trends of vibrational frequencies implicating the moieties containing the X atom, as the X atomic mass is increased, are extrapolated to X = Sn. The results of this extrapolation made it possible to assign the known experimental vibrational frequencies of 3,3-dimethyl-1-(trimethylstannyl)cyclopropene and 3,3-dimethyl-1,2-bis(trimethylstannyl)cyclopropene.

The experimental Raman and IR vibrational spectra of 3,3-dimethyl-1-(trimethylsilyl)cyclopropene in the liquid phase were recorded. Total geometry optimisation was carried out at the HF/6-31G* level and the HF/6-31G*//HF/6-31G* force field was computed. This force field was corrected by scale factors determined previously (using Pulay's method) for correction of the HF/6-31G*//HF/6-31G* force fields of 3,3-dimethylbutene-1, 1-methyl-, 1,2-dimethyl-, and 3,3-dimethylcyclopropene. The theoretical vibrational frequencies calculated from the scaled quantum mechanical force field and the theoretical intensities obtained from the quantum mechanical calculation were used to construct predicted spectra and to perform the vibrational analysis of the experimental spectra.

New olefinic complexes of zerovalent nickel containing 2, 2-dimethyl-1-methylenecyclopropane and 1,3,3-trimethylcyclopropene as ligands and stabilized with triphenylphosphine were synthesized.

The interaction of substituted cyclopropanecarboxylic acid amides with [(Ph3PAu)3O]BF4 (I) has been studied. The reaction of I with cyclopropanecarboxylic acid p-nitroanilide leads to the gold derivative with the AuN bond, the small cycle being unaltered. The interactions between lithiated cyclopropanecarboxylic acid N,N-diethylamides and I afford the organogold derivatives of the amides with gold bonded to the carbon of the small cycle. The compounds obtained were characterized by IR, 1H and 13C NMR spectral data. An X-ray structural study of [triphenylphosphinegold(p-nitrophenyl)carbamoyl] cyclopropane and 1-triphenyl-phosphinegold-1-diethylcarbamoylcyclopropane was carried out. The interaction of lithiated derivatives of cyclopropanecarboxylic acid amides, in excess, with I gives unexpectedly stable anionic complexes of gold(I), (e.g. 1-diethylcarbamoylcyclopropyl)aurate. The potassium salt [(CH2CH2C)CONET2]2AuK is stable in air, and it was isolated after treatment of the lithium salt of bis(diethylcarbamoylcyclopropyl)aurate with potassium carbonate. Its dimeric nature was confirmed by an RDF study, the Au2K2 fragment being a distorted tetrahedron.

Proton-decoupled carbon-13 magnetic resonance spectra of a series of cyclopropane derivatives have been studied. For stereoisomeric substituted 2-phenylcyclopropanes a difference between the isomers has been found in the shieldings of the three-membered cyclic carbons as well as in the shieldings of the carbons of the substituents. The chemical shifts have been interpreted on the basis of an additive approach worked out in a study of the spectra of monosubstituted cyclopropanes and substituted 2,2-diphenylcyclopropanes. Some simple rules have been proposed, which are useful in distinguishing stereoisomeric 1,2-disubstiuted cyclopropanes.

8-Chloro-5-methoxy-3,10-dioxo-1,2,3,4,4aβ,9,9aα,10-octahydroanthracene (Ib) was synthesized; this can serve as an intermediary in the preparation of the tetracyclic analog (IIb) of aureomycin

1. An investigation was made of ways of synthesizing 10-keto-1,2,3,4,4a,9,9a,10-octahydroanthracenes containing various functional groups in the 2- and 3-positions. 2. The compounds obtained may serve as intermediaries in the synthesis of substances related to 6-deoxy-tetracyclines.

Die bei Additionen der Cyclopropene (II) an die Cyclone (I) (Molverhaltnis Cyclopropen:Cyclon 25:1) und (V) (50:l) bevorzugt entstehenden endo-Addukte sind im Gegensatz zu den exo-Isomeren (III) bzw. (VI) thermisch instabil und gehen sofort in die Decarbonylie- . rungsprodukte (IV) bzw. (VII) uber.