Cyclopropanones

Methylideneoxiranes (allene oxides) (80T2269), e.g. (9) and (23), are also highly reactive, and undergo facile thermal isomerization to cyclopropanones, possibly via an oxyallyl intermediate (24 Scheme 20). 

Methylideneoxiranes (allene oxides Section 5.05.3.2.1) react with nucleophiles as if ring opening occurs to give a zwitterion (e.g. 51 or 52), which may be captured by the nucleophile before (Scheme 42) or after (Scheme 43) isomerization to a cyclopropanone. 

IR spectra of diaziridinones show carbonyl absorption at relatively high wave numbers, as found for aziridinones and cyclopropanones, absorbing at 1855-1880 cm (69JOC2254). 

There are several mechanistically related ring expansion reactions of cyclopropanones which lead to /3-lactams. The conversion of cyclopropanone to /3-lactam (174) via the cyclopropanolamine (173) (75JOC1505) is just one modification, but it illustrates the strategy of this type of approach (73TL4855, 69JA2375) which has been applied to the synthesis of 3-amino-nocardicinic acid (81JOC2999). 

FAWORSKI WALLACH Rearrangement Reanangement of a-haloketones or a,a -dihalokeiones to acids or acrylic adds (via cyclopropanones). 

The currently accepted mechanism for the Favorskii rearrangement of dihalo ketones involves a cyclopropanone intermediate formed by loss of HX. This is followed by attack of alkoxide synchronous with cyclopropanone fragmentation and departure of halide ion to form the unsaturated ester... 

The above mechanism would suggest that cyclopropanone formation is synchronous with an internal SN2-type displacement of halogen, with inversion. An alternate pathway assumes loss of halide ion before cyclopropanone formation to give a mesomeric zwitterion or a no bond form of a cyclopropanone which subsequently collapses to the cyclopropanone ... 

In the initial step " the a-halo ketone 1 is deprotonated by the base at the a -carbon to give the carbanion 4, which then undergoes a ring-closure reaction by an intramolecular substitution to give the cyclopropanone derivative 2. The halogen substituent functions as the leaving group ... 

Nucleophilic addition of the base to the intermediate 2 leads to ring opening. With a symmetrically substituted cyclopropanone, cleavage of either Ca-CO bond leads to the same product. With unsymmetrical cyclopropanones, that bond is broken preferentially that leads to the more stable carbanion 5 ... 

Cyclopropanone is highly reactive because of its large amount of angle strain, but methylcyclopropenone, although even more strained than cyclopropanone. is nevertheless quite stable and can even be distilled. Explain, taking the polarity of the carbonyl group into account. 

Conjugated chains, 14, 46 Correlation diagrams, 44, 50 Cyclobutadiene, 171 Cyclobutane, 47, 222 orbital ordering, 26 through-space interactions, 26 Walsh orbitals, 27 Cyclobutene, 200 Cyclohexane, 278 Cyclohexene (half-boat), 274 Cyclopen tadiene, 225 Cvclopen tadienone, 269 Cyclopentadienyl anion, 237 Cyclopentane, 254 Cyclopen ten e, 241 Cyclopropane, 41, 47, 153 construction of orbitals, 19, 22 Walsh orbitals, 22, 36, 37 Cyclopropanone, 48, 197 bond lengths, 38 Cyclopropen e, 49, 132 reactivity, 40... 

Localized orbitals, see bond orbitals and group orbitals Lone pairs, 9, 39, 42, 49 cyclopropanone, 37 methyl fluoride, 42 pyrazine, 28 water, 42... 

Cyclohexanone, 23,35 Cyclohexene oxide, 137 Cyclohcxyl methyl ether, 137 l-Cydohexyl-2-methylpropene, 68-9 ( )-l-Cyclohexyl-2-trimethyl ilylethene, 12 (Z)-l-Cyclohexyl-2-trimethylsilylelhene, 12 l-Cydohcxyl-2-trimethylsilylethyne, 12 (2-Cyclohexylidene-eihyl)trimethylsilane, 29 Cyclopentadec-2-ynone, 48 Cydopentadiene, 25 Cyclopentanone, 72 Cyclopentenones, 15 Cyclopropanone, 133... 

Dibrom-3-oxo-2,4-dimethyl-pentan wird kathodisch (an Quecksilber in aproti-schen Solventien) zu 3-Oxo-2,4-dimethyl-penten-(l) reduziert3. Das intermediar gebil-dete Cyclopropanon-Derivat kann mit Nukleophilen (z. B. Alkoholen, Essigsaure) abge-fangen werden (s. S. 669)3,4. 

Ebenfalls iiber einen Dreiring (Bis-[benzyliden]-cyclopropanon) verlauft die Reduktion von 2,4-Dibrom-3-oxo-l,5-diphenyl-l,4-pentadien in DMF [isoliert wild3-Oxo- 1,5-di-phenyl-penten-(4)-in-( 1)]. In Methanol hingegen bildet sich 5-Oxo-2,3-diphenyl-cydo-penten3. 

In some cases, the two stereoisomers can interconvert. In cis- and trans-disubstituted cyclopropanones, for example, there is reversible interconversion that favors the more stable trans isomer. This fluxional isomerization occurs via ring opening to an unseen oxyallyl valence bond isomer. ... 

Hemiacetals themselves are no more stable than the corresponding hydrates (16-1). As with hydrates, hemiacetals of cyclopropanones and of polychloro and polyfluoro aldehydes and ketones may be quite stable. 

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