Cyclopropanation aromatic compounds

The cyclopropanation of alkenes, alkynes, and aromatic compounds by carbenoids generated in the metal-catalyzed decomposition of diazo ketones has found widespread use as a method for carbon-carbon bond construction for many years, and intramolecular applications of these reactions have provided a useful cyclization strategy. Historically, copper metal, cuprous chloride, cupric sulfate, and other copper salts were used most commonly as catalysts for such reactions however, the superior catalytic activity of rhodium(ll) acetate dimer has recently become well-established.3 This commercially available rhodium salt exhibits high catalytic activity for the decomposition of diazo ketones even at very low catalyst substrate ratios (< 1%) and is less capricious than the old copper catalysts. We recommend the use of rhodium(ll) acetate dimer in preference to copper catalysts in all diazo ketone decomposition reactions. The present synthesis describes a typical cyclization procedure. 

Several organofullerene donor-acceptor molecular material hybrid systems have been synthesized via 1,3-dipolar cycloaddition reactions of azomethine ylides, via Bingel cyclopropanation and methanofullerene formation intermediates as well as via cycloaddition reactions, that have already been discussed in previous sections. The majority of such hybrid systems possess always as acceptor unit the fullerene core and as donor moieties porphyrins, tetrathiafulvalenes, ferrocenes, quinones, or electron-rich aromatic compounds that absorb visible light [190-193]. The most active research topic in this particularly technological field relies (i) on the arrangement of several redox-active building blocks in... 

This process is an important tool in synthetic organic photochemistry for the preparation of small rings. The difficulties in the preparation of medium-size and larger cyclic compounds, caused by entropic factors, have been circumvented by the presence of a rigid molecular scaffold (cyclopropanes, aromatic rings, cyclohexenes and cis-alkenes), which prevents hydrogen abstraction from positions close to the carbonyl group (Scheme 9.39) [64—66]. 

The mechanism of the [3 + 2] cycloaddition is summarized in Scheme The first intermediate results from charge transfer interaction between the eli tronically excited aromatic compound at its singlet state S1 with the alkene w] leads to the formation of the exciplexes K. A more stable intermediate is generated by the formation of two C-C bonds, leading to the intermediates These intermediates have still singlet multiplicity and therefore possess zwii ionic mesomeric structures mainly of type M. In most cases and especially intramolecular reactions, chiral induction occurs during the formation of L. final products are then obtained by cyclopropane formation in the last step. 

The formation of norcaradiene derivatives with naphthalene [reaction (22)] lends some support to this scheme. This mechanism resembles a bimolecular two-step process suggested for the reaction of chloromethyl-aluminum compounds with olefins (199-201). On the other hand, a bimolecular one-step methylene transfer mechanism is generally accepted for the formation of cyclopropane derivatives by the reaction of halo-methylzinc compounds with olefins. This difference between the mechanism proposed for the cyclopropane formation from olefin and that for the ring expansion of aromatic compound may be ascribable to the difference in the stability of intermediates the benzenium ion (XXII) may be more stable than an alkylcarbonium ion (369). 

Whereas Fischer-type chromium carbenes react with alkenes, dienes, and alkynes to afford cyclopropanes, vinylcyclopropanes, and aromatic compounds, the iron Fischer-type carbene (47, e.g. R = Ph) reacts with alkenes and dienes to afford primarily coupled products (58) and (59) (Scheme 21). The mechanism proposed involves a [2 -F 2] cycloaddition of the alkene the carbene to form a metallacyclobutane see Metallacycle) (60). This intermediate undergoes jS-hydride elimination followed by reductive elimination to generate the coupled products. Carbenes (47) also react with alkynes under CO pressure (ca. 3.7 atm) to afford 6-ethoxy-o -pyrone complexes (61). The unstable metallacyclobutene (62) is produced by the reaction of (47) with 2-butyne in the absence of CO. Complex (62) decomposes to the pyrone complex (61). It has been suggested that the intermediate (62) is transformed into the vinylketene complex... 

Conjugation with one or two phenyl groups also converts the cyclopropane ring to an excellent electron donor. Although 1-phenyl- and 1,2-diphenylcyclopropane arguably belong into the category of aromatic compounds, their electron-transfer chemistry is included here, because their reactions are essentially those of cyclopropane compounds. 

Aromatic hydrocarbons, such as benzene add to alkenes using a ruthenium catalyst a catalytic mixture of AuCVAgSbFs, or a rhodium catalyst, and ruthenium complexes catalyze the addition of heteroaromatic compounds, such as pyridine, to alkynes. Such alkylation reactions are clearly reminiscent of the Friedel-Crafts reaction (11-11). Palladium catalysts can also be used to for the addition of aromatic compounds to alkynes, and rhodium catalysts for addition to alkenes (with microwave irradiation). " Note that vinyhdene cyclopropanes react with furans and a palladium catalyst to give aUylically substituted furans. ... 

The reaction has been shown to be of very broad scope with a multitude of nucleophiles Nu such as imides.23,24,29,32,33,36,37,42 amines,10,32 cyanide,25,32 hydroxide,10,32 alkox-ide,10,26,32 electron-rich isocyclic or heterocyclic aromatic compounds,28 carboxamides,31 lactams,31 ureas,31 sulfonamides,31 cyanate,31 formate (to give products with Nu = H),34 C-H acidic compounds,35 hydrazines and hydrazides,38 and sulfinates.38 The amino group NR R2 of cyclopropane-1,1-diamines and the nucleophile Nu in bicycles 8, 9 or 12, respectively, can be easily replaced with other nucleophiles Nu, such as water,10,32,33 alkoxide,10,32-34,42 Grignard compounds,27,42 amines,29,30,36,37,42,43 cyanide,29,33,42,44 hydride,34,42,44 and C-H acidic compounds39-41,43,44 (see Section 5.2.1.). Therefore, it is currently the most important method for the preparation of substituted bicyclic cyclopropylamines. The toxic and costly reagent methyl fluorosulfate can be avoided in a modified synthetic route, which instead of the fluorosulfate 5 proceeds via the corresponding tetraphenylborate, hexafluorophosphate, or (most conveniently) via the tosylate.23 The different steps of the method can often be combined in a one-pot procedure. Results are summarized in Table 3. 

D.ii. Addition to Aromatic Derivatives. Aromatic compounds also react with carbenes, but ring expansion usually follows the initial cyclopropanation. In a typical example, 2-methoxynaphthalene (373) reacted with dichlorocarbene to give 374, and subsequent ring expansion gave 375, 99 which is a general reaction of enol ethers, which give either unsaturated acetals or unsaturated carbonyls. oo... 

Early IR and UV-VIS spectroscopic studies on the formation of carbonium ions from triphenyl methyl compounds on zeolites, titania and alumina were carried out by Karge [111]. In 1979, upon interaction of olefins Hke ethene and propene with zeoHtes CoNaY, NiCaNaY, PdNaY and HY, the appearance of electronic bands between 230 and 700 nm was observed by Garbowski and PraHaud and attributed to an allylic carbenium ion which upon thermal treatment transforms into polyenyl carbenium ions and/or aromatic compounds [112]. These findings were corroborated and extended by studies of the interaction of propene, cyclopropane and frans-butene on zeoHtes NaCoY and HM [30]. In spite of the obscuration of the spectrum in the range between 450 and 700 nm by the threefold spHt d-d band of tetrahedraUy coordinated Co(II) ions in the case of zeoHte NaCoY,the development of bands near 330,385 and 415 nm was assigned to unsaturated carbocations. 

This is a very reactive reagent combination which will cyclopropanate benzene and other aromatic compounds. See Vogel, E. Wiedeman, W. Kiefe, H. Harrison, W. F, Tetrahedron Lett. 1963, 4, 673. Muller, E. Kessler, H. Kricke, H. Suhr, H., Tetrahedron Lett. 1963, 4, 1047. 

The absolute configurations of two sorts of naturally occurring compounds have been determined by X-ray crystallography, and structures of synthetic compounds, all of which contain cyclopropane groups. Compound (4) has been reported as a bisnorcaradiene with a particularly long C-1—C-6 bond (1.80 A). This non-aromatic structure for (4) corroborates earlier n.m.r. work. The cyclopropene moiety of the benzocyclopropene (5) has been shown ... 

Substitution reactions of CgFsSCl and / -MeCeHgSCl with aromatic compounds and active-methylene compounds represent a separate area of sulphenyl halide chemistry. A related process, the ring-opening of the cyclopropane moiety of quadricyclanes by PhSCl, has been studied. ... 

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