Cyclopropane derivatives vinyl, rearrangement

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. 

The effect of substituents at both vinylic termini is demonstrated by the 1,2 3,4 rearrangements of cyclopropane derivatives 24 and 261006. Substrate 24 smoothly rearranges to trans-hy-droazulene 25, but a temperature of 220 °C is required for the rearrangement of 26. Due to the boat transition state with the vinyl moieties folded back over the cyclopropane and the eclipsed orientation of the substituents, drastic reaction conditions are necessary for 26 to adopt the reacting conformation. 

The light-induced rearrangement reactions of trivinyl methanes to give divinyl cyclopropane and vinyl cyclopentene derivatives are known as the tri-n-methane rearrangements. The reaction involves both singlet and triplet excited states. For... 

The next question to be answered was whether or not substituents other than phenyl at that position could also promote the reaction. Therefore, the study was extended to aldehydes 31 and 32, with differently substituted vinyl units at the y-position. Previously we have observed efficient 1-ADPM rearrangement of the corresponding oxime acetates, showing that the substitution pattern present in 31 and 32 was suitable for promoting DPM reactivity. Triplet-sensitized irradiation of 31, for 15 min, afforded the ODPM product 33 (52%) as the trans-isomer exclusively and starting material (42%), as shown in Scheme 7. Similarly, irradiation of 32, for 20 min, under the same conditions used for 31, yielded starting material (30%) as a 3 2 mixture of ,Z-isomers and the cyclopropane derivative 34 (47%) as a 8 1 mixture of ,Z-isomers (Scheme 7). ... 

If a bromomethyl- or vinyl-substituted cyclopropane carbon atom bears a hydroxy group, the homoallyiic rearrangement leads preferentially to cyclobutanone derivatives (J. Sa-laun, 1974). Addition of amines to cydopropanone (N. J. Turro, 1966) yields S-lactams after successive treatment with tert-butyl hypochlorite and silver(I) salts (H.H. Wasserman, 1975). For intramolecular cyclopropane formation see section 1.16. 

Small amounts of cyclopentene derivatives are detected in cyclopropanation reactions of electron-deficient dienes, but they may result from thermal rearrangement of the corresponding vinyl cyclopropanes and not from a direct [4+1] cycloaddition... 

Use of chiral cyclopropylethynyllithium derivatives permits the elegant selective synthesis of labeled chiral vinylcyclopropanes, for stereochemical studies of the thermal vinyl cyclopropane-cyclopentene rearrangement. Thus, reductive elimination of (15, rra )-(2,2-dibromoethenyl)-l-methylcyclopropane with BuLi in pentane, followed by hydrolysis of the lithium acetylide, afforded (15, rraw5)-2-ethynylmethylcyclopropane (equation 157). 

MO calculations have been carried out on the isomerization of cyclopropane to propene, and the MNDO method has been used to study the reaction pathway and to optimize the structure of reactant, transition structure, and product of the ring opening reaction of bicyclo[1.1.0]butane. Various methods have been employed to estimate the rate constants for ring opening of the 2-cyclopropyl-2-propyl radical. 1-Acceptor-1-sulfenyl-substituted 2-vinylcyclopropanes of the type (430) have been found to afford 6-sulfenyl-a,jS y, -unsaturated carboxylic esters and nitriles (431) upon treatment with acid, by a process which involves C(l)—C(2) bond fission and a novel 1,5-sulfenyl rearrangement (see Scheme 110). It has been shown that the benzophenone-sensitized photolysis of vinyl norcaradiene derivatives, such as 5-(2-methylprop-l-enyl)-3-oxatricyclo[4.4.0.0 ]deca-7,9-dien-4-ones (432), results in the regioselective cleavage of only one of the cyclopropyl c-bonds to afford isochroman-3-one derivatives (433). It has been reported that the major product obtained from the reaction of structurally diverse a-diazo ketones with an electron-rich alkene in the... 

Prior chapters have covered the use of transition metals in asymmetric hydrogenations ( 6.2 and 7.1), hydroborations ( 7.3), hydrosilylations and hydro-cyanations ( 6.3, 6.4, 7.4 and 7.5), cyclopropanations ( 7.19), aldol reactions ( 6.11), allylations of carbanions ( 5.3.2), and some sigmatropic rearrangements ( 10.3). This chapter covers other reactions catalyzed by transition metal complexes including coupling of organometallic reagents with vinyl, aryl or allyl derivatives, Heck reactions allylamine isomerizations, some allylation reactions, car-bene insertions into C-H bonds and Pauson-Khand reactions. 

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