Allenes cyclopropanation

The reaction of PTAD with allenic cyclopropanes 83 gives high yields of the pyrazolotriazoles 84.132 The reaction has been extensively studied, and... 

Cyclohexan (Cyclopropyliden-methylen)- E17b, 1493 (Br2—cyclopropan -> Allen) Cyclopropan... 

Cerny and co-workers measured calorimetrically heats of hydrocarbon adsorption on Pt (243) and Dy (244) films at room temperature. The heats of adsorption on Pt were significantly higher than those found in the previous study and increased in the order methane ethylene < propylene < acetylene methylacetylene < allene < cyclopropane ethane < propane. 

The rhodium-cataiyzed intramoiecuiar [5+2] cycioaddition of an allene and vinylcyclopropane was the key step in the asymmetric total synthesis of the trinorguaiane sesquiterpene (+)-dictamnol by P.A. Wender and co-workers.The cyclization precursor allene-cyclopropane was assembled starting from commercially available cyclopropane-carbaldehyde. Using the HWE oiefination, the Weinreb s amide moiety was installed and subsequently reacted with a primary alkyllithium that was generated via lithium-halogen exchange. 

PTAD reacts with allenic cyclopropane derivative (356) to give high yields of a mixture in which pyrazolotriazoles (357) and (358) predominate (Equation (54)) <71JA2562, 73JA1553, 74JA6220, 74JA6944>. 

Ruden et al calculated the indirect nuclear spin-spin coupling constants of allene, cyclopropane, and cyclopropene at different levels of electronic-structure theory and compared them with experimental equilibrium constants, which were obtained from experiment by subtracting evaluated vibrational contributions. It was found that, even in a relatively small basis set, the coupled-cluster singlesand-doubles (CCSD) method provides very good results. SOPPA consistently performed better than RASSCF. Hybrid DFT performed as well as SOPPA for the one-bond coupling constants, while, for the other coupling constants, it provided results of similar quality as CCSD. 

The process of transfer of one hydrogen atom from an allylic alkene (an ene) to an electrophilic alkene (an enophile) followed by formation of a new cr-bond and migration of allylic double bond is known as ene reaction or Alder ene reaction [1]. The ene may be an alkene, alkyne, allene, cyclopropane ring or arene, whereas an enophile may be an alkene, carbonyl, thiocarbonyl, imino or diazo compound having an electron withdrawing substituent. Oxygen may also serve as an enophile. The reaction usually takes place from left to right, since a new [Pg.161]

Dibromocarbene has been successfully generated under phase transfer conditions and added to a variety of olefmic substrates. These include isolated double bond systems, styrenes, conjugated dienes, allenes, cyclopropanated olefins, vinyl ethers, allylic halides, and enynes. It is interesting to note that with the latter class of compounds, dibromocarbene addition to double bonds appears to be favored over addition to triple bonds. The simple addition of dibromocarbene according to equation 4.1 to a number of substrates is recorded in Table 4.1. 

Cyclopropanations of alkenes with alkyl diazoacetates are catalysed by rhodium(ii) carboxylates, and Sasaki et al have shown that crown ethers have several advantages over quaternary ammoniurq ions for the catalytic synthesis of allene-cyclopropanes from addition of allene-carbenes to olehnic substrates. 

Lankin and co-workers reported the photochemical reaction of aUylallene. - Direct irradiation (254 nm) of fra s-7-phenyl-2,5,5-trimethylhepta-2,3,6-triene 116 in r-butyl alcohol leads to the formation of methylene bicyclo[2.1.0]pentane 117 and allenic cyclopropane 118, along with trans,cis-isomerization product 119. Similarly, the irradiation of the cis-isomer 119 also affords 117 and 120 with cis,trans-isomerization product 116. No di-it-methane rearrangement to cyclopropanes is observed in these reactions. On the basis of quenching studies, the triplet states of trans- and cis-trienes 116 and 119 are indicated to be chemically significant excited states in the formation of bicyclo[2.1.0]pentane 117. The photochemical reaction of vinylallene 121 was reported by Maier and co-workers to afford intramolecular cyclization product 122, and 122 also yields allene 121 photochemicaUy. ... 

Ethyl chrysanthemate (ethyl 2,2-dimethyl-3 c and t -[2-methylpropenyl]-cyclopropane carboxylate) [97-41-6] M 196.3, b 98-102 /llmm, 117-121 /20mm. Purified by vacuum distn. The free trans-acid has m 54° (from, EtOAc) and the free cis-acid has m 113-116° (from EtOAc). The 4-nitrophenyl ester has m 44-45° (from pet ether) [Campbell and Harper J Chem Soc 283 1945 IR Allen et al. JOrg Chem 21 29 1957]. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Die Reduktion geminaler Dibrom-cyclopropane mit Chrom(II)-acetat in Dimethylsulf-oxid fiihrt (in Abhangigkeit von Zeit und Temperatur) zu wechselnden Mengen an Brom-cyclopropanen. Aus 2,2-Dibrom-1,1-diphenyl-cyclopropan entsteht dagegen ausschlieB-lich 1,1 -Diphenyl-allen (s. S.517), in waBr. Dimethylformamid entstehen zusatzlich Aeetoxy-Derivate4 ... 

Investigation of Ethane, Propane, Isobutane, Neopentane, Cyclopropane, Cyclopentane, Cyclohexane, Allene, Ethylene, Isobutene, Tetramethylethylene, Mesitylene, and Hexamethylbenzene. Revised Values of Covalent Radii (by Linus Pauling and L. O. Brockway)... 

The reaction between CHCI3 and OH is often carried out under phase-transfer conditions. It has been shown that the reaction between PhCHCl2 and t-BuOK produces a carbenoid, but when the reaction is run in the presence of a crown ether, the free PhCCl is formed instead.Dihalocyclopropanes are very useful compoundsthat can be reduced to cyclopropanes, treated with magnesium or sodium to give allenes (18-3), or converted to a number of other products. 

Fig. 15. Newton diagram in velocity space for Y+cyclopropane at Eco = 18.5 kcal/mol. Larger solid circle corresponds to maximum velocities for YCH2 products, while smaller solid circle and smaller dotted circle correspond to maximum velocities for Y-propyne and Y-allene products, respectively. Lab angular distributions for YCH2 (open squares) and YC3H4 (open circles) recorded under identical collision conditions. Solid-line fits to lab angular distributions generated using CM distributions in Fig. 17.

Some remarks concerning the scope of the cobalt chelate catalysts 207 seem appropriate. Terminal double bonds in conjugation with vinyl, aryl and alkoxy-carbonyl groups are cyclopropanated selectively. No such reaction occurs with alkyl-substituted and cyclic olefins, cyclic and sterically hindered acyclic 1,3-dienes, vinyl ethers, allenes and phenylacetylene95). The cyclopropanation of electron-poor alkenes such as acrylonitrile and ethyl acrylate (optical yield in the presence of 207a r 33%) with ethyl diazoacetate deserve notice, as these components usually... 

The cyclopropanation of a-allenic alcohols 616 gave methylenecyclop-ropanes 617a, b and spiropentanes 618a, b in different proportions depending on the carbenoid reagent used (Scheme 88) [163,4b]. 

Transition metals 172 a-bonded to cyclopropanes, substituted on the a-carbon with a halogen atom, are interesting intermediates for cyclopropylidene complexes 173 or allene ones 174 [88]. The former complexes are also supposed to be precursors of the above-mentioned nickel enolates. (Scheme 65)... 

An interesting variation appears when furan reacts with the allenic carbene generated by the action of potassium ter-butoxide upon l-bromo-3,3-dimethylallene. Though the yield is only 9%, one product is reasonably assigned a structure (Scheme 52) that could hardly be approached by way of a cyclopropane intermediate. The authors comment that in an allenic carbene in the singlet state two electrons will be accommodated in the sp... 

Hexamethyl[3]radialene (25) does not undergo Diels-Alder-reactions with the typical electron-poor dienophiles, probably because of the full substitution at the diene termini. With TCNE, however, a violet-blue charge-transfer complex is formed which disappears within 30 min at room temperature to form a 1 1 adduct (82% yield) to which structure 55 was assigned9. Similar observations were made with tris(2-adamantylidene)cyclopropane (34), but in this case cycloaddition product 56 (81% yield) was identified its allenic moiety is clearly indicated by IR and 13C NMR data12. 

The discovery of carbene and carbenoid additions to olefins was the major breakthrough that initiated the tapping of this structural resource for synthetic purposes. Even so, designed applications of cyclopropane chemistry in total syntheses remain limited. Most revolve around electrophilic type reactions such as acid induced ring opening or solvolysis of cyclopropyl carbinyl alcohol derivatives. One notable application apart from these electrophilic reactions is the excellent synthesis of allenes from dibromocyclopropanes 2). 

Reaction of Me3GeCl with a substituted cyclopropene in the presence of lithium diisopropylamide (LDA) yields different products depending on the order of addition of the reagents.97 Addition of LDA to a mixture of the reactants gives the dimetallated cyclopropene (Equation (76)). Dilithiation of the cyclopropane followed by addition of Me3GeCl gives the allene (Equation (77)). 

The [3,3]-sigmatropic rearrangement ofpropargyl esters [234, 561] is usually an equilibrium reaction for example steric repulsion can help to deliver mainly the allene [562] and faster reaction kinetics are observed with silver(I) and copper(I) catalysts [562-571] (see cyclopropane 169 in Scheme 1.75) [572], and recently also rhodium(I) catalysts [573]. 

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