Synthesis of Cyclopropyl Ethers and Cyclopropanols by Carbene Transfer – Acetolysis of Cyclopropyl p-Toluenesulfonates

The reaction of chloromethyl phenyl ether with butyllithium in olefins yields phenoxy-cyclopropanes. 1-Chloro-1-phenoxycyclopropanes can be prepared in a similar manner, though the yields are poor. Alkoxycyclopropanes are formed when dichloromethyl alkyl ethers are treated with methyllithium/lithium iodide in the presence of olefins. Cyclopropanols can be obtained in good yields by reaction of (β-chloroethoxy)cyclopropanes either with butyl- or ethyllithium or with bases. – As was shown by acetolysis experiments with cyclopropyl p-toluenesulfonates having a known steric configuration, the rearrangement of a cyclopropyl derivative into an allyl cation proceeds in accordance with the Woodward-Hoffmann-DePuy rule. The solvolysis of exo-bicyclo[n.1.0]alkyl p-toluene-sulfonates is assumed to proceed via “semi-open” intermediates, which are somewhere between an allyl cation and a cyclopropyl cation.     

Stereoconvergent Generation of a Contrasteric syn‐Bicyclopropylidene (=syn‐Cyclopropylidenecyclopropane) by Stille‐Like Coupling

Stereoisomerically pure endo‐ and exo‐7‐halo‐7‐(trimethylstannyl)benzonorcar‐3‐enes (=endo‐ and exo‐(1‐halo‐1a,2,7,7a‐tetrahydro‐1H‐cyclopropa[b]naphthalen‐1‐yl)trimethylstannane) 4 and 6 were selectively obtained by lithium? tin or magnesium? tin transmetalation in good yields (Scheme 2 and 3). The reaction of these compounds with copper(I) thiophene‐2‐carboxylate (CuTC) produced in both cases the corresponding C_S‐symmetric bicyclopropylidene (=cyclopropylidenecyclopropane) syn‐ 1 , a single diastereoisomer (Schemes 5 and 6). The structure of syn‐ 1 was undoubtedly elucidated by X‐ray single crystal diffraction. The coupling mechanism of the carbenoid cyclopropane is discussed (Scheme 7).     

One-pot synthesis of multisubstituted quaterphenyls and cyclopropanes

An efficient one-step synthetic route toward multifunctionalized quaterphenyls 3 or cyclopropanes 4 is developed from substituted chalcones 1 and sulfones 2 in good yields via a regioselective [3C+3C] or [1C+2C] annulation. The reaction features mild conditions, multisubstitution, and functional groups tolerance and is transition metal catalyst-free. The protocol provides a novel alternative to the conventional methodologies for the synthesis of quaterphenyls or cyclopropanes.     

The Synthesis of a New Class of Potential Inhibitors for Glycoside Hydrolases†

Some attempts toward the synthesis of novel inhibitors of glycosyl transferases are described. More successfully, the synthesis of an activated cyclopropacyclohexene and an amide and an amine of a cyclopropa‐fused pyranose are described. None of these three novel compounds proved to be a significant inhibitor of a retaining α‐glucosidase from barley.     

Synthesis and reactions of hydroxyspiro[5.2]cyclooctenones based on the cyclization of the dianions of acetone and diethyl 2-oxopropylphosphonate with 1,1-diacylcyclopropanes

The cyclization of the dianions of diethyl 2-oxopropylphosphonate and of acetone with 1,1-diacylopropanes afforded hydroxyspiro[5.2]cyclooctenones which were transformed, by homo-Michael reactions with tetrabutylammonium halides, into various functionalized phenols or their dimers.     

Spectroscopic Studies of 1-Aryl-2,2-Dichlorocyclopropanes

Seventeen 1-aryl-2,2-dichlorocyclopropanes were examined by using IR, ¹³C NMR, and mass spectrometry. The data obtained from IR and ¹³C NMR spectra indicate that the bond strength of carbon-chlorine on the cyclopropane ring and the electron density of that carbon depend on the substituent. The mass fragmentation patterns of compounds in this series resemble those of the dibromo analogues. The fragmentation mechanism is proposed to involve the formation of indenium ion through an electrocyclization.     

High temperature bromination. Part 22: Bromination of 1a,2,7,7a-tetrahydro-1H-cyclopropa[b]naphthalene

The high-temperature bromination of 1a,2,7,7a-tetrahydro-1H-cyclopropa[b]naphthalene and its carboethoxy derivative was studied. Reaction of the title compound with 1 mol of bromine in refluxing carbon tetrachloride resulted in the formation of ring-opening products. In the case of the carboethoxy derivative, bromination took place both regio- and stereospecifically at the benzylic positions, the cyclopropane ring did not undergo bond cleavage. A mechanism for the formation of the products and their dehydrobromination reactions is discussed.     

Homoallyl-Substituted Vinylcyclopropanes from α,β-Unsaturated Ketones and Allylindium Derivatives

Simply reversing the order of addition of aqueous acid and Et₂O to the Barbier intermediate 1 of the known indium-mediated allylation leads to unprecedented deoxygenative rearrangements [Eq. (a)].     

Dimethyl(2-oxo-2-ferrocenylethyl)sulfonium iodide—a useful synthetic equivalent of ferrocenoylcarbene in the synthesis of ferrocene-containing cyclopropanes

The reaction of 1-ferrocenyl-3-thiabutan-1-one with methyl iodide in acetonitrile at room temperature gave dimethyl(2-oxo-2-ferrocenylethyl)sulfonium iodide, which was characterized by spectral data (¹H NMR, ¹³C NMR, IR) and X-ray crystallographic analysis. This salt reacted with a base (sodium hydride) in acetonitrile yielding a stabilized ylide—dimethylsulfonium ferrocenoylmethylide, which was in turn, submitted to reactions with seven conjugated enones. The obtained results showed that this methodology is potentially a new and useful approach to ferrocene-containing cyclopropanes.     

C11-Chirasil-Dex as chiral stationary phase in GC: enantioselective separation of cyclopropane derivatives

Chirasil-β-Dex containing an undecamethylene spacer (C11-Chirasil-Dex) was used as chiral stationary phase (CSP) in enantioselective gas chromatography (GC). The versatility of the new stationary phase in the simultaneous enantiomeric separation of a set of cyclopropane derivatives is demonstrated. The GC method provides information about the chemical yields of the cyclopropane products, enantioselectivity, substrate specifity, and catalytic activity of the chiral catalysts used in the intermolecular cyclopropanation of olefins and avoids time-consuming work-up procedures.