Carbonyl compounds cyclopropyl

Cyclopropyl carbonyl compounds, SbF, promotes condensation of a, -enones with a-diazo carbonyl compounds to form 1,2-disubstituted cyclopropyl carbonyl compounds. BF3 etherate or TiF4 is much less efficient. The reaction is subject to steric hindrance by substituents on the vinyl group. SbFs also promotes isomerization of the initial trans-cis mixture of products to the more stable isomer. ... 

The ring contraction of 1,2-cyclobutanediones is promoted either by acids or by bases in protic media". The reaction products are a-hydroxycyclopropanecarboxylic acids or the corresponding esters. Rearrangements of some 2-alkylidenecyclobutanols to cyclopropyl carbonyl compounds are also known. 1,2-Epoxycyclobutanes afford cyclopropanecarbal-dehydes or cyclopropyl ketones under the catalytic action of protic acids, lithium iodide or lithium thiocyanate (equation 107) . Under the latter conditions, the reaction... 

In contrast the trans, trans acid (222) was deprotonated at the benzylic position to give the allyl anion (224), which upon protonation gave as expected, 225. It has not been possible to prove the existence of the cyclopropyl anions 219 and 223 (only in the case of the methyl ester enolates the cyclopropyl anion corresponding to 219 has been shown by deuteration to exist at — 78°C). Thus, deprotonation of cyclopropyl carbonyl compounds may be strongly dependent on the structural details of the cyclopropane, as previously demonstrated by the relative acidities of 209 and 210. 

Ring contraction of 2-alkylidenecyclobutanois to cyclopropyl carbonyl compounds.2 2-Methylenecyclobutanol (1) is converted quantitatively into 1-methyl-cyclopropanecarboxaldehyde (2) when treated with 5 % H2S04 at 100° for 30 min. the rearrangement can be induced by heat treatment in a sealed tube at 245° for 4 hr. The... 

Cyclopropyl sulfones were shown to be obtained either by cyclization of y-p-tosyloxy sulfones 232 with base or by treatment of phenylsulfonylacetonitrile 233a or ethyl phenyl sulfonyl acetate 233b with 1,2-dibromoethane in the presence of benzyltriethyl-ammonium chloride (BTEA) and alkali in good yields. Chang and Pinnick synthesized various cyclopropane derivatives 234 upon initial treatment of carbanions derived from cyclopropyl phenyl sulfone with either alkylating agents or a carbonyl compound and subsequent desulfonylation, as shown below. 

Larger changes in bond lengths, as expected, are observed for more localized carbocations. Most of the structures available are for stabilized systems, such as protonated carbonyl compounds [e.g. the protonated cyclopropyl ketones referred to on page 110 (Childs et al., 1990), and dioxacarbocations (Paulsen and Dammeyer, 1973, 1976 Paulsen and Schuttpelz, 1979 Childs et al., 1986, 1991). It is normal to see one of the atoms of the counterion (in most cases MXJ or MX ) packing in the position expected for addition to the activated C=OH(R)+ system, apparently just within the sum of the van der Waals radii for the neutral centres (Childs et al., 1986). This can happen without significant pyramida-lization, however (Childs et al., 1991), and on both sides of the planar carbon centre it tells us little new about reactivity. 

Direct evidence for triplet-triplet transfer has been provided by sensitizing both the isomerization of cis- or ira/w-olefins,28 38 79,80 and the dimerization of some cyclic olefins81-83 with carbonyl compounds. Furthermore, the phosphorescence of some carbonyl compounds can be quenched by olefins (for example, acetone with 2-pentene30 and phenyl-cyclopropyl ketone with 2-methyl-2-butene37). On the other hand, the phosphorescence of benzophenone is not quenched by 2-methyl-2-butene37 nor is the photoreduction of benzophenone quenched efficiently by cyclohexene (Table II). 

Bis(cyclopropyl)titanocene is prepared from cyclopropyllithium and dichloroti-tanocene in 95% yield. The complex has been utilized as an olefination reagent in reactions with a wide variety of carbonyl compounds, including esters, furnishing the corresponding methylenecyclopropane derivatives (equation 13). ... 

The TiCU-induced three-component coupling reaction of an a-haloacylsilane, allylsilane and another carbonyl compound gives 48 in good yield. A silyl enol ether intermediate is suggested (equation 31)82. The reaction of a cyclopropyl ketone with allylsilane yields a mixture of skeletal rearranged products83. 

In intermolecular PET processes, radical ions are formed either as close pairs or as free species from neutral molecules (Sch. 1) [2,6]. Most commonly, carbonyl compounds or related derivatives as for example enol ethers, cyclopropyl ketones, and siloxycyclopropanes are used for intramolecular cyclization reactions. With the exception of cycloadditions the ring-building key step is always an intramolecular bond formation. In PET... 

Reaction with cyclopropyl alcohols and ketones. The primary and secondary cyclopropyl alcohols 1 and 2 are converted by reaction with P2I4 or PI, mainly into the corresponding iodides. In contrast, the tertiary a-cyclopropyl alcohol 3 is converted into the homoallylic iodide 4 under very mild conditions. a-Cyclopropyl aldehydes and ketones are also cleaved by P2I4 to -y-iodo carbonyl compounds in high yield, particularly when the solvent is acetone. 

In a similar fiashion to the Collins reagent, PCC will also induce oxidative rearrangement of tertiary allylic alcohols (Table S). PCC, and several other chromium oxidants, will also cause tertiary cyclopropyl alcohols to rearrange to give 3,y-unsaturated carbonyl compounds (equation 8). ... 

Carbonyl compounds can also act as the nncleophtles in intermolecular processes with 1,6-enynes. Thus, the gold(I)-catalyzed reaction between enynes and aldehydes or acetone gives stereoselectively tricyclic compounds (equation 71). The transformation is mechanistically intriguing, as it proceeds by a rearrangement of the initially formed cyclopropyl gold carbene (the intermediate in the donble-cleavage mechanism), which is then trapped by the carbonyl compound to form the products. 

Further evidence for singlet 1,4-diradical intermediates has been obtained in the case of photocycloaddition of cyclopropanecarbaldehyde with ( )-penta-1,3-diene, in which the formation of the cyclopropyl-oxetane (PS) dominated. This is in contrast to the case of aromatic carbonyl compounds and cyclopropylethylene in which the formation of considerable amounts of ring-opened products and ox-epins, formed by cyclopropylcarbinyl-allylcarbinyl rearrangement, implicates the intermediacy of a triplet 1,4-diradical. ... 

Although reaction of a,/3-unsaturated carbonyl compounds with diazo compounds generally gives cyclopropyl compounds in low yields, in the presence of SbFs, the cyclopropanation of a,)8-unsaturated carbonyl compounds with diazocarbonyl compounds proceeds very well to produce the desired products in good yields (Eq. 22) [41]. 

The reactivity pattern exhibited by jS-oxycyclopropyl-a-carbonyl compounds revolves chiefly around the selective fragmentation of the C-C bond situated between the oxy and carbonyl substituents, by virtue of the possible transmission of electron density between donor and electron units. Well defined polar intermediates, that is, zwitterionic species, are likely to intervene in some cyclopropyl-carbonyl transfigurations. 

A classical method using Na- or Li-liquid ammonia (Birch reduction conditions) is effective for reductive dehalogenations of aryl and vinylic halides, but it is not always successfully applied to alkyl halides, although cyclopropyl halides and bridgehead halogens are exceptions.Under such conditions, the reactions are often accompanied by side reactions, such as elimination, the Wurtz coupling reaction, cyclization and reduction of carbonyl compounds. An example, a synthesis of pentaprismane (1), is shown in Scheme 4. ... 

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