Alkenes, -cycloaddition with cyclopropanes

The highly strained nature of methylene- and alkylidenecyclopropanes has been evidenced by spectroscopic measurements and X-ray analysis. The presence of the exocyclic double bond imposes a lengthening of the C(2)-C(3) bond as a result of an increase of the C(2)-C(l)-C(3) angle (compared to cyclopropane). This structural feature is reflected in a typical reactivity of these compounds which is a thermal or transition metal catalysed [3 + 2] cycloaddition with alkenes. This chemistry, usually referred to as TMM chemistry , has been the object of many studies and thoroughly reviewed by Binger and Buch [2] and Trost [8]. 

W(CO)6 in toluene at room temperature gave the tricyclic adduct 190a in 94% yield after acidic workup. This reaction forms the tungsten-containing azomethine ylide 191, which undergoes the [3 + 2]-cycloaddition with 189a. The rhodium(n)-catalyzed cyclization of the ene-yne-aldimine 192 with alkene 193 into the cyclopropane 194 was reported by Uemura and Ohe (Scheme 32).42c... 

Dicarbonyl(ri5-cyclopentadienyl)iron-alky] complexes represent useful precursors for iron-carbene complexes [47]. For example, iron-carbene complexes are intermediates in the acid-promoted reaction of Fp-alkyl ether derivatives with alkenes to provide cyclopropanes via a [2 + l]-cycloaddition (Scheme 1.16). 

Various cyclic compounds are prepared by the reaction of these carbene complexes with various unsaturated compounds [78-80]. The metallacyclobutane 246 is generated by [2+2] cycloaddition with electron-rich alkenes, and its reductive elimination affords the cyclopropanes 247. 

Michael-aldol reaction as an alternative to the Morita-Baylis-Hillman reaction 14 recent results in conjugate addition of nitroalkanes to electron-poor alkenes 15 asymmetric cyclopropanation of chiral (l-phosphoryl)vinyl sulfoxides 16 synthetic methodology using tertiary phosphines as nucleophilic catalysts in combination with allenoates or 2-alkynoates 17 recent advances in the transition metal-catalysed asymmetric hydrosilylation of ketones, imines, and electrophilic C=C bonds 18 Michael additions catalysed by transition metals and lanthanide species 19 recent progress in asymmetric organocatalysis, including the aldol reaction, Mannich reaction, Michael addition, cycloadditions, allylation, epoxidation, and phase-transfer catalysis 20 and nucleophilic phosphine organocatalysis.21... 

Radical iodine atom transfer [3 + 2]-cycloaddition with alkene (118) using dimethyl 2-(iodomethyl)cyclopropane-l,l-dicarboxylate (117) forms cyclopentane derivative (119), through the formation of an electron-deficient homoallyl radical, followed by the addition to alkene, and cyclization via 5-exo-trig manner as shown in eq. 4.41. 

In these C-H insertion reactions, the similarity with cyclopropane formation by intramolecular cycloadditions to alkenes is clear, and the mechanisms mirror one another quite closely. As with the cyclopropanation reactions, the path of the reaction differs according to whether the carbene is a singlet or triplet. Singlet carbenes can insert in a concerted manner, with the orbitals overlapping constructively provided the carbene approaches side-on. 

R and R may be H, methyl, cyclopropyl, cyano, or ester groups. The phenylcarbene formed on irradiation of trans-l,2-diphenyloxirane has been trapped and identified in the form of a cyclopropane derivative in methanol in the presence of benzyl methyl ether and alkenes. Photolysis in the presence of 2,3-dimethyl-2-butene proceeds by cycloaddition with the formation of cyclopropane-carboxylic acid and oxetane derivatives (Eq. 368). ... 

Recently, this methodology has been expanded towards the synthesis of 1-substituted vinylcyclopropanes. Thus, heating 0.5-1 equivalent of the appropriate cyclopropenone acetal in a dry aromatic solvent to 80-150°C for 30-48 h in the presence of an electron-deficient alkene afforded a cyclopropane. This was isolated after hydrolysis of the ketene acetal moiety. The [1-1-2] cycloaddition proceeded with a high degree of regio- (>92 8) and stereoselectivity (> 84 16), depending on the substituents (see table below). ... 

Many gew-diarylcyclopropanes have been synthesized photochemically from alkyl-substituted alkenes and diaryldiazomethanes. The outcome of the reaction is most sensitive to the alkene structure either cycloaddition to give cyclopropanes or abstraction-recombination to give alkenes can dominate. Thus, photochemically generated diphenylcarbene reacts only by cycloaddition with propene, but exclusively by abstraction-recombination with 2,3-dimethylbut-2-ene.39.90,9) alkyl-substituted alkenes undergo both types of reaction and, as a result, most 1,1-diaryIcyclopropanes are formed in moderate )deld. 

Trialkylsiloxyallylidene)cyclopropanes 58, prepared from the corresponding ketones 57, underwent facile cycloadditions with activated alkenes and alkynes to give 59 and 60, respectively (Table 6). The enol ethers were hydrolyzed directly upon aqueous workup. 

Menthol [(—)-l] has been used as a chiral ligand for aluminum in Lewis acid catalyzed Diels-Alder reactions with surprising success2 (Section D.l.6.1.1.1.2.2.1). The major part of its application is as a chiral auxiliary, by the formation of esters or ethers. Esters with carboxylic acids may be formed by any convenient esterification technique. Esters with saturated carboxylic acids have been used for the formation of enolates by deprotonation and subsequent addition or alkylation reactions (Sections D.l.1.1.3.1. and D.l.5.2.3.), and with unsaturated acids as chiral dienes or dienophiles in Diels-Alder reactions (Section D. 1.6.1.1.1.), as chiral dipolarophiles in 1,3-dipolar cycloadditions (Section D.l.6.1.2.1.), as chiral partners in /(-lactam formation by [2 + 2] cycloaddition with chlorosulfonyl isocyanate (SectionD.l.6.1.3.), as sources for chiral alkenes in cyclopropanations (Section D.l.6.1.5.). and in the synthesis of chiral allenes (Section B.I.). Several esters have also been prepared by indirect techniques, e.g.,... 

The [3-1-2] cycloaddition is mostly catalyzed by Ni or Pd catalysts. The MCPs can have substituents on the olefin or cyclopropane, and the two-atom partners can be electron neutral or deficient alkenes, alkynes, and carbon-heteroatom multiple bonds. Since there are different reaction courses of MCP in cycloaddition, introducing substituents on either MCP or the two-atom reaction partners complicates the reaction even more, considering the associated selectivity issues. Consequently, cycloaddition with multi-substituted substrates often gives mixtures though sometimes good selectivity can be achieved by adjusting reaction conditions and substituents. The intramolecular version of [3-1-2] cycloaddition, mainly developed by Motherwell [81], Nakamura [82], Lautens [83], and Mascarenas [87-91], may address the issues of selectivity to some extent, and leads to polycyclic structure meanwhile. AU these have been summarized by several excellent reviews [1, 84—86] and herein we will only update the [3-1-2] cycloaddition of MCP for synthesis of carbocycles with some recent representative examples. 

The Lewis-acid-promoted formal intramolecular 3 + 2-cycloaddition of cyclopropane 1,1-diesters with allenes (25) produced [4.3.0]nonanes (26) and [3.2.1]octanes (27) by parallel-cycloaddition and cross-cycloaddition, respectively (Scheme 8). Similarly, the Lewis-acid-catalysed formal intramolecular 3 + 2-cycloaddition reactions of cyclopropane 1,1-diesters with alkenes produced bridged[n.2.1]carbocyclic compounds with excellent stereo- and regio-selectivity under mild conditions. This reaction has been successfully applied to the total synthesis of tetracyclic diterpenoids phallocladanol and phallocladene. ... 

---