Vinylcyclopropane derivatives

Electron-deficient 1,3-dienes are known to react when heated with metho-xy(aryl)- or methoxy(alkyl)carbene complexes to afford vinylcyclopropane derivatives with high regioselectivity and diastereoselectivity [8a, 24]. Cyclo-propanation of the double bond not bearing the acceptor functional group and... 

The reaction of alkenylcarbene complexes and electron-poor alkenes normally leads to mixtures of the expected [2S+1C] vinylcyclopropane derivatives (see... 

Ferrate 38 also turned out to catalyze [5 + 2]-cycloadditions. In this context, various vinylcyclopropane derivatives 52 were converted into the corresponding cycloheptadiene derivatives 53. The products were obtained in good to excellent diastereoselectivites favoring the 1,2-trans-disubstituted isomer 53a. 

The low yields obtained with extremely strong bases, LDA and NaH, suggested the formation of another reactive intermediate. Therefore, the reaction was carried out in the presence of methyl acrylate as a Michael acceptor and afforded a new adduct 35 in addition to the expected vinylcyclopropane derivative 33 (see Equation 8). 

Parti. The Malonate Condensation with 1.4-Dibromobut-2-ene. A Convenient New Route to Vinylcyclopropane Derivatives. J. chem. Soc. [London] 1952, 3610. 

If the double bond is connected directly to the three-membered ring, i.e. if the substrate is a dihalo-vinylcyclopropane derivative, a vinylcyclopropylidene to cyclopentadiene isomerization, the so-called Skattebol rearrangement, takes place upon treatment with alkyllithium. Again, this ring-forming step competes with a ring-destruction process leading to allenic hydrocarbons (vinylallenes,... 

One of the classical papers in this area is Neureiter s discovery of the vinyl-cyclopropane to cyclopentene rearrangement [185]. This important process was first observed on a l,l-dichloro-2-vinylcyclopropane derivative, which on heating yielded a chlorocyclopentadiene, presumably by the loss of hydrochloric acid from the initially formed 4,4-dichlorocyclopentene. 

Other methods leading to ring enlargement utilize low-valent iron complexes such as Fe(CO)5, as was shown by Taber and coworkers in the ring expansion of vinylcyclopropane derivatives 55 under carbonylating conditions to give the cyclo-hexenone derivatives (Scheme 9.43) as a 5.9 1 mixture of the 2,5- (56) and the constitutional isomer, the 2,6-substituted cydohexenones [101, 102],... 

While the nucleophilic addition of 1-lithio-l-bromocyclopropanes to ketones gave oxaspiropentanes, precursors of 1-donor substited vinylcyclopropane derivatives vide supra, Sect. 4.5, Eq. (28)), addition of n-BuLi at low temperature to 1,1-di-bromocyclopropane 199 (prepared in 75 % yield from the addition of dibromocarbene... 

Even in vinylcyclopropane derivatives in which the vinyl group is anti to the CH group, thermolysis often leads to 1,4-dienes as a result of isomerization to the syn isomer, followed by l,S-shift (e.g. equation 17). ... 

Dinnocenzo and Conlon have described the remarkable effect of one-electron oxidation on the rate of certain vinylcyclopropane rearrangements. Exposure of several l-p-anisyl-2-vinylcyclopropane derivatives to a catalytic amount of tris(4-bromophenyl)aminium hexafluoroantimonate in acetonitrile at room temperature was found to induce ring expansion to form cyclopentenes (equation 25) temperatures in excess of 200 °C are required for the conventional thermal rearrangement cf these systems. At this time it is uncertain whether these reactions follow concerted mechanisms, or are stepwise processes involving trimethylene cation radical intermediates. 

When electron deficient alkenes are added to cyclopropene derivatives (74 equation 33) and (77 equation 34) in the presence of [Ni(COD)2], vinylcyclopropanes are formed in good yields. For example, dialkyl fumarate or maleate reacts with 3,3-dimethylcyclopropene in the presence of [Ni(COD)2] to give 2,3-bis(alkoxycarbonyl)-l-(2-methyl-l-propenyl)cyclopropanes (75), (76), (78) and (79), in which alkene stereochemistry is chiefly retained, in 50-73% yields. Reaction of methyl acrylate with 3,3-dimethylcyclopropene results in the formation of several products, while reaction of methyl acrylate with 3,3-diphenylcyclopropene gives vinylcyclopropane derivatives (80 equation 35) in 85% yield. Under similar conditions, methyl crotonate reacts with (74a) to give (82) in low yield (equation 36). Catalysis with nickel(0)/PR3, 2 [Ni(CO)4], 3 [Pd(DBA)2] or [Pd(DBA)2]/PlV33 gives mainly... 

Vinylcarbene is also regarded as an intermediate in the catalytic isomerization of cyclopropene in the presence of [CuCl P(OPh)3 ]. 3-Methyl-3-cyclopropylcyclopropene (83a) and 3,3 dicyclo-propylcyclopropene (83b) react with cyclopentene derivatives under die influence of CuCl/P(OPh)3 to yield cntfo-vinylcyclopropane derivatives (84 equation 37) in 55-72% yields. 3-Methoxycarbonyl-l-propylcyclopropene also reacts with noibomadiene in the presence of CuCl to give the corresponding vinylcarbene adducts in 60% yield. 

In a large number of carbene and carbenoid addition reactions to alkenes the thermodynamically less favored syn-isomers are formed 63). The finding that in the above cyclopropanation reaction the anti-isomer is the only product strongly indicates that the intermediates are organonickel species rather than carbenes or carbenoids. Introduction of alkyl groups in the 3-position of the electron-deficient alkene hampers the codimerization and favors isomerization and/or cyclodimerization of the cyclopropenes. Thus, with methyl crotylate and 3,3-diphenylcyclopropene only 16% of the corresponding vinylcyclopropane derivative has been obtained. 2,2-Dimethyl acrylate does not react at all with 3,3-dimethylcyclopropene to afford frons-chrysanthemic add methyl ester. This is in accordance with chemical expectations 69) since in most cases the tendency of alkenes to coordinate to Ni(0) decreases in the order un-, mono-< di- < tri- < tetrasubstituted olefines. 

With hexene-1 and heptene-1, the yields of vinylcyclopropane derivatives are rather low (5-10 %), the main products being the corresponding hexatriene derivatives. With the other alkenes listed above, the yields of cyclopropanation products range from 55 to 7%67). 

Armesto and co-workers have reported the photochemical behaviour of the vinylcyclopropane derivatives (98) under w-methoxyacetophenone sensitisation in methylene chloride as the solvent. A variety of products are formed, the nature of which is dependent upon the substituent on the cyclopropyl ring. The key intermediate is believed to be the biradical (99) that is formed following energy transfer. A study of the effect of wavelength on the outcome of the irradiation of (100) has been reported. At short wavelengths (250 and 254 nm), it is thought that the S2 state of (100) is populated and this results in the formation of the three products (101), (102) and (103) in a ratio of 6 1 1. 

Thus, 1-hydroxycyclopropanecarboxylic acid provided an efficient and convenient precursor to 1 -donor-substituted 1 -vinylcyclopropane derivatives, whose high synthetic potential has been recently explored. It allows the easy preparation of hydroxy-protected (silyl- or acetal derivatives) 1 -hydroxycyclopropanecarbaldehyde. so- ... 

Photolysis of 6-methylcholesta-3,5-diene in pentane/ethanol (1 4) gave two isomeric vinylcyclopropane derivatives 6-methyl-3jS,5-cyclo-5 -cholest-6-ene (1,40%) and 6-methylene-3jS,5-cyclo-5j9-cholestane (2,20%). In addition, two ethyl ethers, 3a-ethoxymethyl-6-methyl-y4-norcholest-5-ene (3,17%) and 6)S-ethoxy-6a-methyl-3j8,5-cyclo-5) -cholestane (4, 5%) were formed. ... 

It should also be mentioned that a number of vinylcyclopropane derivatives have been prepared by prototropic migration of a C-C double bond remote from the cyclopropane ring, but this reaction will not be discussed here. 

Cyclobutane formation, occasionally in fairly low yield due to ring-opening reactions, also occurred by photochemical [2 - - 2] cycloaddition of vinylcyclopropane derivatives to an a, -unsaturated ketone moiety, " a cyclobuta-1,3-diene, a 1,4-benzoquinone, 2-acylthiophenes, and on irradiation of e t/o,enr/o-2,4-bis[( )-2-(methoxycarbonyl)vinyl]bi-cyclo[1.1.0]butane. A formal [2-1-2] cycloaddition also occurred on reaction of tricyclo[3.1.0.0 ]hex-3-ene with methyl 6-oxo-5-phenyl-l,3,4-oxadiazine-2-carboxylate to give methyl 9-oxo-10-phenyl-8-oxapentacyclo[4.4.0.0 ". 0 .0 °]decane-7-carboxylate, albeit in very low yield, after nitrogen extrusion. ... 

The addition of malonates and related C-H acidic compounds to activated vinylcyclopropanes has also been performed with tetrakis(triphenylphosphane)palladium(0) rather than sodium alkoxide. ° The primary products 12 arising from the 1,7-addition can react with a second molecule of the vinylcyclopropane derivative in the same fashion to give afford 1 2 adducts 13. 

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