Cyclopropane acid catalyzed

Synthesis of a-alkoxyketones from a-diazocarbonyl compounds and alcohols under the influence of copper or rhodium catalysts is well established as an alternative to the Lewis or proton acid catalyzed variant of this synthetic transformation. The sole recent contribution to the aspect of general reactivity deals with the competition between O/H insertion and cyclopropanation of unsaturated alcohols 162). The results... 

Related halomethylzinc alkoxides, which are monomeric in solution, were studied for their effectiveness in cyclopropanation reactions. The Lewis acid-catalyzed reaction is the only reaction pathway at low temperature and... 

The product possesses a homoallylic stannane moiety, which can be utilized as a useful synthon for cyclopropane formation (Scheme 68). Upon treatment of the homoallylstannane with HI, destannative cyclization takes place to give cyclopropylmethylsilane.271,272 A Lewis acid-catalyzed reaction with benzaldehyde dimethyl acetal affords vinylcyclopropane.273... 

Cyelobutanone has been prepared by (1) reaction of diazomethane with ketene,4 (2) treatment of methylenecyclobutane with performic acid, followed by cleavage of the resulting glycol with lead tetraacetate,s (3) ozonolysis of methylenecyclobutane, (4) epoxidation of methylene-cyclopropane followed by acid-catalyzed ring expansion,7 and (5) oxidative cleavage of cyclobutane trimethylene thioketal, which in turn is prepared from 2-(co-chloropropyl)-l,3-dithiane.8... 

As previously mentioned, Davis (8) has shown that in model dehydrocyclization reactions with a dual function catalyst and an n-octane feedstock, isomerization of the hydrocarbon to 2-and 3-methylheptane is faster than the dehydrocyclization reaction. Although competitive isomerization of an alkane feedstock is commonly observed in model studies using monofunctional (Pt) catalysts, some of the alkanes produced can be rationalized as products of the hydrogenolysis of substituted cyclopentanes, which in turn can be formed on platinum surfaces via free radical-like mechanisms. However, the 2- and 3-methylheptane isomers (out of a total of 18 possible C8Hi8 isomers) observed with dual function catalysts are those expected from the rearrangement of n-octane via carbocation intermediates. Such acid-catalyzed isomerizations are widely acknowledged to occur via a protonated cyclopropane structure (25, 28), in this case one derived from the 2-octyl cation, which can then be the precursor... 

Anodic oxidation of alkyl substituted cyclopropanes and spiroalkanes in methanol/TEATos (tetraethyl ammonium tosylate) affords monomethoxy and dimethoxy products in yields ranging from 6 to 86% [30, 31]. The products result from the cleavage of the most highly substituted C,C bond. In contrast to the anodic cleavage the acid-catalyzed cleavage occurs selectively at the less substituted carbon. The cleavage of hetero-substituted cyclopropanes is reported in Ref [32-35]. 

Acid-catalyzed dealkoxylation is particularly suitable for the preparation of highly reactive, cationic iron(IV) carbene complexes, which can be used for the cyclopropanation of alkenes [438] (Figure 3.11). Several reagents can be used to catalyze alkoxide abstraction these include tetrafluoroboric acid [457-459], trifluoroacetic acid [443,460], gaseous hydrogen chloride [452,461], trityl salts [434], or trimethylsilyl triflate [24,104,434,441,442,460], In the case of oxidizing acids (e.g. trityl salts) hydride abstraction can compete efficiently with alkoxide abstraction and lead to the formation of alkoxycarbene complexes [178,462] (see Section 2.1.7). 

Sie, S.T. (1993) Acid-catalyzed cracking of paraffinic hydrocarbons 2. Evidence for protonated cyclopropane mechanism from catalytic cracking experiments. Ind. Eng. Chem. Res., 32, 397. 

Charette and Brochu have reported an alternate protocol for the Lewis acid-catalyzed cyclopropanation reaction of allylic alcohols, in which the uncatalyzed process is suppressed . The addition of Zn(CH2l)2 (1 equivalent) to an allylic alcohol (1 equivalent)... 

One major advantage of the alkoxymercuration-demercuration approach to ethers over the acid-catalyzed process is the fact that carbon skeleton rearrangements are seldom observed. Only unsaturated cyclopropanes,42S>426 or aryl-substituted alkenes427 428 in the presence of highly electrophilic mercury salts afford rearranged products. 

The oxidative ring opening of 3-oxabicyclo[4.1.0]hept-4-enes, formed by the intramolecular Pt(ll)-catalyzed cyclopropanation of enol ethers by alkynes, gives oxepane derivatives. Alternatively, the acid-catalyzed opening of the cyclopropane ring leads to dihydrobenzofurans or 3,4-dihydro-2//-chrorncncs <20040L3191>. 

Acid-catalyzed seven-membered ring formation to afford the first stable A-oxo-2,1 -benzoxazepinium ions has been reported, based on reaction of l-chloro-2-(2-nitrobenzyl)cyclopropane with H2S04 and FSO3H nitro group trapping of an intermediate carbocation was proposed in this process <1996ZOR852>. 

Reaction of the enol ether 58 with dimethyl diazomalonate provides the spiro compound 59 in high yield. Reduction and acid catalyzed cyclopropane cleavage gives the unsaturated y-lactol 60 which can be oxidized to p-methylene y-butyro-lactone 61 20). 

Liao and Wei took advantage of the possibility of photochemically rearranging cyclohexa-2,4-dienones into bicyclo[3.1.0]hexenones in their approach to synthetically useful cyclo-pentenones such as 135 [6, 160-162]. This approach was based on the acid-catalyzed cyclopropane ring-opening of bicyclo[3.1.0]hexenones such as 134, as generated photochemically from non-dimerizing ortfio-quinone monoketals such as 133 (Figure 33) [165]. 

The acid-catalyzed cyclization of appropriate aryloxyketones formed benzo[l,2-6 5,4-6 ]difuran and benzo[ 1,2-6 4,5-6 ]difuran (63BSF1003). Another variation involved the cyclization of an aryl thioacetal to a benzo[l,2-6 4,5-6 ]dithiophene <86CB3198>. In investigations of the synthesis of a unit of the CC-1065 skeleton (see Section 7.21.12), a carbene derived from the azo-compound (59) constructed the cyclopropano-fused benzodipyrrole (60) by simultaneous formation of the heterocyclic ring and the cyclopropane ring <83TL4773>. 

The catalyst causes a classical carbenium ion to be formed by acid catalyzed activation reactions. The classical carbenium ion is transformed into the key intermediate which can be described as a protonated cyclopropane structure. After some rearrangements cracking occurs. The formation of branched paraffins is very fortunate since branched paraffins have high octane numbers and the isobutane produced can be used in alkylation. The preferred products are those of which the formation proceeds via tertiary carbenium ions. Carbenium ions can also be generated by intermolecular hydride transfer reactions between alkane and carbenium ions that are not able to form tertiary carbenium ions (see Chapter 4, Section 4.4). Under more severe conditions lower paraffins can also be cracked. 

The skeletal isomerization of C4 and C5 n-olefins is an acid-catalyzed reaction requiring relatively strong acid sites that proceeds via carbenium ion intermediates formed upon protonation of the double bond (17). Double bond cis-trans isomerization usually occurs on the acid sites before skeletal isomerization. The general reaction mechanism for branching isomerization is depicted in Fig. 2 2. Protonation of the double bond leads to a secondary carbenium ion, which then rearranges into a protonated cyclopropane (PCP) structure. In the case of n-butenes,... 

The versatile selenenylating agent N-(phenylseleno)phthalimide (NPSP) is an effective carbocyclization mediator, which is capable of effecting acid catalyzed cyclization reactions from open-chain olefins, including the formation of cyclopropanes This is demonstrated by the quantitative cyclization of 3-butenyltrimethyltin to (cyclopropyl-methylseleno)benzene upon treatment with 1.1 equivalents of NPSP in CH2CI2 at 25 °C under acid (e.g. p-TsOH) catalysis (equation 47) . ... 

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