Cyclopropane derivatives cyclopropanes, photoreactions

The photoelimination of nitrogen from 1-pyrazolines is one of the most thoroughly investigated photoreactions and it has been used extensively in the synthesis of cyclopropane derivatives.334 Both stereospecific and non-stereospedfic processes have been observed and these are believed, at least in simple 1-pyrazolines, to correspond to singlet and triplet excited states, respectively. Two reaction pathways have been proposed in the azoalkane 405335 direct excitation via a thermally activated S, state affords the C6H6 isomers 406 to 409, whereas triplet-sensitized excitation results in a tem-... 

To examine the viability of CIM a number of photoreactions (electrocyclic reactions, Zimmerman (di-n) reaction, oxa-di-7i-methane rearrangement, Yang cyclization, geometric isomerization of 1,2-diphenyl-cyclopropane derivatives, and Schenk-ene reaction) which yield racemic products even in presence of chiral inductors in solution have been explored (Sch. 40) [187,189-200]. Highly encouraging enantiomeric excesses (ee) on two photoreactions within NaY have been obtained photocyclization of tropolone ethylphenyl ether (Eq. (1), Sch. 40) and Yang cyclization of phenyl benzonorbornyl ketone (Eq. (3), Sch. 40). The ability of zeolites to drive a photoreaction that gives racemic products in solution to ee >60% provides... 

Irradiation of the E-isomer of (70) brought about E-Z isomerization as well as cyclization by group migration to the cyclopropane derivatives (71). These derivatives were also photoreactive and ring-opened to the alkenes (72). The kinetics of the photorearrangement of the benzocycloheptene (73) has been studied in detail. Irradiation in methanol affords the six products shown in Scheme 5, and solvent dependence in the reaction was investigated. 

The effect of substituents on the temperature dependence of a-carbonyl-carbene reactivity has been examined using carbenes generated by low-temperature photolysis of methyl diazophenylacetate. A correction to the literature on the photoreaction of isopropylidene diazomalonate (98) with 1,3,3-trimethyl-cyclohexane (99) has been reported. The photoproduct, originally thought to be a cyclopropane derivative, has now been shown to be the cyclobutanone (100), the formation of which presumably involves a photo-Wolff rearrangement as illustrated in Scheme 11. Substituent effects observed in the product distribution of diazo-amide photochemistry have been ascribed to conformational factors the jS-lactam, oxindole, and Wolff rearrangement products appear to arise directly from the excited singlet state of the sym-Z form of the diazo-amide itself. 

As in previous years, much time and effort have been devoted to the study of the photochemistry of cyclic azo-compounds. Photoreactions of this type offer a unique opportunity to examine the mechanism of this decomposition, and also provide a useful synthetic route to cyclopropane derivatives. Irradiation of several steroidal 4 S,5-dihydro[17a, 16-c]pyrazoles leads exclusively by elimination of nitrogen to cyclopropa[16a,17a] compounds.6 The penicillin derivatives... 

Sarel and co-workers have examined some reactions of alkynylcyclopropanes with iron carbonyl compounds [1]. Treatment of cyclopropylacetylene (5) with iron pentacarbonyl under photolytic conditions gives, after cerium(IV) oxidation, isomeric quinones 6 and 7, derived from two molecules of 5 and two carbonyls with both cyclopropane rings intact [6]. Furthermore, the photoreaction of dicyclopropylacetylene (8) with iron carbonyl gives some ten different products depending on the reagents and the reaction conditions, and some of them have the cyclopentenone skeleton formed by the opening of cyclopropane ring coupled with carbonyl insertion [7] (Scheme 2). 

Exposure of several methyl-substituted derivatives to y-radiolysis at 77 K in cryogenic matrices gave rise to a family of radical cations of the same structure type, some of which had been previously identified on the basis of CIDNP results. We begin with a discussion of the CIDNP investigations, since they preceded the ESR studies of all species but the prototype. The first CIDNP results attributed to a cyclopropane radical cation were observed during the photoreaction between 1,4-dicyanonaphthalene and cis-l,2-diphenylcyclopropane. However, the nature of the cyclopropane radical cation was characterized by CIDNP effects observed during the reaction of chloranil with cis- and /rans-l,2-diphenylcyclo-propane. ... 

The aminocyclopropane derivative 374 and the propellane 372 were obtained, each in 26 % yield, by photocycloaddition of 370 and ethylene in acetone . Diradicals 371 and 373 were suggested as intermediates in the photoreaction (equation 90). The use of isobutene or 2,3-dimethyl-2-butene instead of ethylene gave no cyclopropane product . 

Anthraquinonecarboxamide in its Sj state will photoadd two molecules of water. The photoreactions of diphenylhomobenzoquinones in the presence of amine donors have been studied. 1-Bromo substituted diphenylhomobenzoqui-none irradiated in the presence of triethylamine induces opening of the cyclopropane ring with formation of 2-diphenylmethyl-5-methyl-l,4-benzoquinone, and with dimethylaniline, a mixture of an aminated bicyclic dione and bis(p-dimethyl-aminophenyl)methane is produced. Irradiation of boron difluoride complexes derived from 1,3-diketones can lead to a number of different types of process, in particular exciplex formation and slow cycloaddition. Evidence has now been advanced to suggest that excitation of these complexes leads directly to an exciplex without the participation of an encounter complex, and that this solvolyses to free ions. 

ELECTRON TRANSFER PHOTOREACTIONS OF CYCLOPROPANE AND SPIROPENTANE DERIVATIVES... 

Osuka etaL described the type 11 photoreaction of various homonaphthoquinones 22a-d with abstractable y-hydrogens. The photochemical behavior of these substrates is very dependent on the cyclopropane substituents (R and R ). Irradiation of 22a (R = H, R = CH,) gave the usual cyclobutanol 23a along with the unsubstituted alcohol 24a (Scheme 14). The compound 24 may be derived by hydrogen transfer from a 8-carbon to the less reactive ketyl radical center of the primary biradical VII. It was confirmed that a photoequilibrium takes place between 22 and 23 via VII as a common intermediate. 

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