Ring-opening reaction of cyclopropyl

Scheme 3.44. General scheme of domino radical ring-opening reactions of cyclopropyl ketones...

The ring-opening reaction of cyclopropyl radical [Equation (7)] was shown to occur at 174°C to give ally radical, but the product stereochemistry was unclear. Ab initio direct dynamics study was carried out to clarify the stereochemical course of the reaction.40 Trajectories were initiated at the ringopening TS obtained at CASSCF(3,3)/6-31G(d), with quasiclassical normal sampling at the experimental temperature of 174°C. ZPE was included, and thermal vibrational energy was sampled from the normal-mode Boltzmann distribution. A rotational energy of RT/2 was added toward the allyl radical product. 

The stereospecific ring-opening reactions of cyclopropyl derivatives have played a key role in establishing selection rules for pericyclic processes . Extensive and conclusive evidence has been presented in support of DePuy s initial postulation that disrotatory ringopening and C-X bond heterolysis are synchronous processes, and all kinetic , stereochemical and theoretical findings lend credence to the DePuy-Hoffmann-Wood ward rule Substituents on the same side of the 3-membered ring as... 

The generally slow conrotatory ring-opening reaction of cyclopropyl anions as compared to the fast isomerization of the corresponding allyl anions has been supported by means of MO calculations with the parent anions (Table 31) . 

A mixture of THF and DMPU has been used as a solvent for Sml2 in various reactions such as cyclization of alkynyl halides [90,91], tandem iodo-enone cy-clization/samarium enolate aldol reaction [92], coupling of (3-silylacrylic esters [93], deprotection of arenesulfonamides [94] and pyridine-2-sulfonamides [95], radical ring-opening reactions of cyclopropyl ketones and the trapping of the resulting samarium(III) enolates by a variety of electrophiles [96] (Scheme 41). 

Scheme 7. Ring opening reactions of cyclopropyl radicals [198].

Ferrier-rearrangement-based ring-opening reactions of cyclopropylated sugar derivatives also find attractiveness, especially in the case of functionalized oxepane formation. With the emergence of the methods described in Section 13.2.8, in addition to cyclization, methodologies of linear precursors offer now a reasonable number of synthetic methods to prepare oxepanes and septanoses. 

Perhydrofuro[2,3- ]pyrans can be synthesized via a ring-opening reaction of sugar derivatives containing a 1,2-cyclopropyl group <20070L1331>. 

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... 

Bicyclic cyclopropyl compounds are anodically dimethoxylated to give stereoisomeric cis and trans) cyclopropane ring-opened products, as in Eq. (48) [322]. Shono and coworkers [323] reported a different type of ring-opening reaction of a cyclobutyl compound through anodic methoxylation. They also found that anodic oxidation of borneol and isoborneol in methanol resulted in a rearrangement to provide methoxylated stereoisomeric products with the same endo-exo ratio, as in Eq. (49) [324] ... 

The rates of the ring-opening reactions of the cyclopropyl anions 10 and 14 have also been compared with the rate of the forbidden disrotatory ring-opening reaction of the structurally related cyclopropyl anion 15 (to give 16) which was introduced by Wittig and coworkers 19,13). 

A peculiar ring-opening reaction of 1,1,2,2-tetramethoxycyclopropane, rather than isomerization, with zinc(II) iodide is knownT Rearrangement of the cyclopropyl cation to the allyl cation may account for the ring opening. 

Palladium-catalyzed ring-opening hydrosilylation of cyclopropyl ketones formed (Z)-enol silanes (Scheme 2.79) [131]. The mechanism is proposed to proceed via oxidative cyclization, ring contraction, transmetalation, and reductive elimination. In contrast, the rhodium-catalyzed reaction afforded mixtures of cyclopropanes and ring-opened products [132]. 

In the presence of (la), aryl cyclopropyl ketones react with aromatic aldehydes to afford a,p-unsaturated ketones (66) [103a]. The proposed mechanism includes a ring-opening reaction of (la)-activated cyclopropyl ketones by nucleophilic attack of ambient H2O and subsequent aldol reaction with aromatic aldehydes. When a-ketoesters are used instead of aldehydes, 5,6-dihydropyran-2-ones (67) are formed by the pathway including the transesterification between the intermediate (68) and a-ketoesters (Scheme 9.39) [103b]. 

The ring-opening reaction of functionalized 1,2-cyclopropyl carbohydrates is also known, apart from that of unfiinctionalized derivatives. Yu and Pagenkopf demonstrated the formation of oxepine 51 through Ferrier rearrangement-based ring opening... 

The most frequently encountered examples of cyclopropyl ring opening reactions in the steroid field are usually associated with angular or side chain methylation sequences. In fact, isotope labeling of the C-19 angular methyl group is the only reported application of this reaction for deuteration or tritiation pui poses. 

It is known that ketones, which are capable of aldol condensation, react with trichlorogermane in a particular way. First, an aldol condensation occurs and then trichlorogermane adds to the C=C double bond of the product of condensation74. However, in the case of methyl cyclopropyl ketone, the condensation does not occur and a single isomer derived from the ring opening reaction is formed with 65% yield (equation 28)75. 

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