Cyclopropenone

There is a suhstantial difference in dipole moments between methylenecyclopro-pene and cyclopropenone. but the difference between fnlvene and eyclopentadie-none is much smaller. Explain. 

C. Calculate the dipole moment of cyclopropenone using the OPTIONS input to change the 1.1 matrix element to 2.0 for electronegative oxygen. Use the results to infer the direction of the dipole moment toward or away from the oxygen atotn. 

Cyclopropenones and cyclobutendiones can be photolyzed or thermolyzed (FVP) to give acetylenes. 

Cyclopropenones react with nitrosobenzene by an O-initiated attack at C-1 to produce isoxazolin-5-ones (75TL3283, 78USP4053481), and an isoxazolin-5-one was produced as a by-product in the photolysis of nitroethylene (78AJCU3). Substituted oxazolin-5-ones have... 

Cycloadditions of aziridines to diphenylcyclopropenone lead to 4-oxazolines (36) (70CJC89). A mechanism involving initial addition to the cyclopropenone carbonyl group followed by ring opening and recyclization was suggested. 

NMR measurements on 2,3-fluorophenylthiirene 1-oxides and 1,1-dioxides show that electron withdrawing conjugative effects are greater for the sulf one than for the sulfoxide and that both are less conjugated than cyclopropenones <79JA390). 

The vertical ionization potentials from the photoelectron spectra of some thiirane and thiirene derivatives are given in Table 3. A Walsh localized scheme of bonding is generally preferred. There is a strong hyperconjugative interaction in thiirene 1,1-dioxides between the occupied C=C tt-MO and the occupied SO2 pure sulfur d-AO. Thiirene oxides are suggested to be less aromatic than cyclopropenones and tropone. 

Oxidative ring expansion occurs when the hydrazine (175) is treated with manganese dioxide (73TL4091). Diphenylcyclopropenone (176) reacts with ammonia and methylamine to give /3-lactams (69BCJ1777). Initial attack could occur at either C-1 or C-2 of the cyclopropenone. 

Cyclopropenone prepared in this way is quite pure and suitable for most chemical purposes. It can he repurified by crystallization from 3 volumes of ethyl ether at — 60° using a cooled filtering apparatus. The residual ethyl ether is then removed by evaporation at 1-2 mm. and 0° very pure cyclopropenone is obtained in 60-70% recovery from the above distilled material. 

The product usually contains small amounts of ether, as judged by proton magnetic resonance. The yields given are based on pure cyclopropenone ketal. Proton magnetic resonance (chloroform-d) B (number of protons, multiplicity) 7.88 (2, singlet), 3.33 (6, singlet). 

The bath temperature should be raised slowly to prevent decomposition of cyclopropenone. 

Cyclopropenone was flrst synthesized " by the hydrolysis of an equilibrating mixture of 3,3-dichlorocyclopropene and 1,3-dichloro-cyclopropene (prepared by reduction of tetrachlorocyclopropene with tributyltin hydride). This procedure has been adapted - to prepare... 

There have been extensive physical and chemical studies of cyclopropenone, cyclo-pentadienone, and cycloheptatrienone (tropone). The results of these studies can be briefly summarized as follows ... 

The reaction of the ethynylestradiol derivative (50) with difluorocarbene represents an equally fascinating series of reactions. The major product obtained in 48% yield is the difluorocyclopropene (51). The latter is hydrolyzed to the cyclopropenone (53), and is readily alkylated at C-21 to (54), which is also obtained by difluoromethylation of the propynyl derivative (57). The cyclopropenone (53) loses carbon monoxide at elevated temperature to... 

Care should be taken to prevent either the dibromoketone or the cyclopropenone from coming into contact with the skin, as allergic reactions have been observed in several cases. The use of gloves is recommended especially for the bromoketone. The latter product has a wide melting range because it is a mixture of the meso- and d,/-compounds. 

The structural features and the spectroscopic characteristics of the thiirene dioxide system (22) are of special theoretical interest since, on the basis of analogy with cyclopropenone (23), it is a possible nonbenzenoid aromatic system with all the physical and chemical implications involved. Aromatic and/or conjugative effects, if any, require transmission through the d-orbitals of the sulfur atom. 

On the basis of a naive analogy with cyclopropenones, the ground-state aromatic stabilization of which has been recently reconfirmed, some kind of aromaticity can, in principle, be assigned to these systems when Z = SO or S02, assuming a possibility for transmission of electronic effects via -conjugation. 

The 13C NMR data for representative three-membered sulfones and sulfoxides are given in Table 5. The chemical shifts of the sp3-hybridized a-carbon in the parent thiirane70 and the five-membered ring86 sulfide, sulfoxide and sulfone are 18.1, 31.7, 54.3 and 51.1, respectively, whereas those of cyclopropenone, diphenylcyclopropenone and dimethylcyclopropenone are 169.087, 148.788 and 157.9, respectively. 

The [3S+1C] cycloaddition reaction with Fischer carbene complexes is a very unusual reaction pathway. In fact, only one example has been reported. This process involves the insertion of alkyl-derived chromium carbene complexes into the carbon-carbon a-bond of diphenylcyclopropenone to generate cyclobutenone derivatives [41] (Scheme 13). The mechanism of this transformation involves a CO dissociation followed by oxidative addition into the cyclopropenone carbon-carbon a-bond, affording a metalacyclopentenone derivative which undergoes reductive elimination to produce the final cyclobutenone derivatives. 

Diphenyl-cyclopropenon ergibt nach Reaktion mit Diboran und Protonolyse mit Bu-tansaure in 45%iger Ausbeute cis-1,2-Diphenyl-cyclopropan9 ... 

---