Reactions involving Cyclopropane Rings

The naphthalene-sensitized isomerization of 1,2-diarylcyclopropanes has been the subject of several investigations during the past few years. The most recent study has examined the isomerization of c/s-l, 2-diphenylcyclopropane sensitized 

The discovery of a real photochemical homoallylic rearrangement of 2-aryl-cyclopropylcarbinyl acetates (32) and (33) has been reported.28 In cyclohexane the products formed [from (32a)] are the corresponding m-cyclopropane and the homoallyl product [(34), 25%] (minor amounts of benzylcyclohexane and 1-phenyl butadiene were also detected). Acetone sensitization shows that the 

Direct irradiation ( = 250 nm) of the allylcyclopropane (37) yielded five products, viz. 1,1-diphenylethylene 1,1-diphenyl-2 2-dimethylethylene 1,1-di-phenyl-4-methylpenta-l,3-diene 1,1-diphenylbuta-l,3-diene and the vinyl-cyclobutane (38). Independent photolysis of the vinylcyclobutane (38) shows that it photochemically fragments into l,l-diphenyl-2,2-dimethylethylene and 

The text of a lecture dealing with the di-w-methane reaction has been published.30 Zimmerman31 has discussed the use of stereochemical changes as probes for the mechanism of photochemical reactions. 

Di-7r-methane reactions have been reported for the aryl olefins (39).32 In all cases studied the product was the arylcyclopropane (40). The formation of the products was sensitive to the nature and position of the substituent on the aryl ring. These results, and the fact that the quantum yield for product formation is higher in cyclohexane than in acetonitrile, suggest that the biradical intermediate (41) might be important in the transformation. An excited singlet-state mechanism is proposed. 28 

A study of the di-Ti-methane reactivity of the barrelene derivatives (73) in zeolites has been published. The reaction in a slurry affords a 77 23 mixture of (74) and (75) when the reaction is carried out in a zeolite the cyclooctatetraene product is suppressed and the two products are obtained in a ratio of 1 99. This enhancement of the di-Ti-methane reactivity occurs with Li - and Na -exchanged zeolites.Liao and co-workers have reported new reactivity of some barrelenes. The reactions encountered are sensitive to substitution pattern. Thus, the irradiation of (76) with electron withdrawing groups follows the di-TT-methane route, to yield (77) and (78) predominantly. The less heavily substituted derivative (79) behaves differently, and irradiation affords (80) and (81) by the aza-di-7r-methane rearrangement, with (82) formed only in small amounts by the alternative di-Ti-methane path. Calculations have been used to examine the mechanism of the barrelene-semibullvalene isomerization. These results indicate that two biradical intermediates are involved in the T state. Other calculations on the di-Ti-methane rearrangement of barrelene substantiate the Zimmerman mechanism for the sensitized rearrangement. 

Zimmerman and Novak have continued the search for further examples of the tri-7i-methane process. Some of the systems studied are illustrated by (83). Sensitized irradiation of these compounds brings about the di-7r-methane reaction affording (84) and (85). The tri-Ti-product (86) is not formed under sensitized conditions, and direct irradiation is needed to produce this product. A secondary product (87) is also formed. The regioselectivity of the process was studied in detail. 

Steady state and laser-flash photolysis have been used to study the photochemical transformation of the barrelene derivative (47). Irradiation of this in a 

The di-TT-methane reactivity of the allylphenanthrene (46) has been studied. Both direct ((/ = 0.043) or xanthene-sensitized ( p = 0.053) irradiation gives the cyclopropyl derivative (47). This compound is also photoreactive, and on direct irradiation ( ()= 0.091) is converted into the phenanthrylbutene (48). The sensitized reaction in this case is extremely inefficient ( ( = 0.0007). 

The acetophenone-sensitized photorearrangement of the benzonorbor-nadiene (49) yielded the tricycloheptene (50a) as the exclusive product. Analogous products (50b—d) were also formed by sensitized irradiation of the cyclopropene derivatives (51a—c), respectively. 

Cristol ef a/. have demonstrated that the sensitized conversion of the dibenzobarrelene (52a) into the semibuUvalenes (53) and (54) does not show a sensitizer energy effect. A similar lack of dependence was shown for the conversion of the isomer (52b) into (55) and (53). The authors suggest that the product-determining step occurs after energy transfer and that the selectivity is not due to the formation of an exciplex. Direct irradiation of the 

Kuzuya, M- Adachi, A. Noguchi, and T. OJcuda, Tetrahedron Lett., 1983, 24, 2271. 

A study has demonstrated the utility of the photocyclization of vinylstilbene derivatives (74) to the tricyclodecatrienes (75).  

The irradiation of the optically active dibenzbarrelene (72) in solution affords the four isomeric products (73 a-d). The ratio of products formed (73)(a+b) (73)(c+d) is 55 45. Irradiation of a single crystal affords the same four products but in a ratio of 90 10 when the conversion was kept to 25 %. The results obtained show that there is no chiral selectivity in the solution phase conversion but that there is a preference for the formation of one of the regio isomers (73 a.b). The solid state reaction is considerably different and affords the regio isomer (73a) in high optical purity (80 % enantiomeric excess).  

A review has discussed the photochemical reactivity of small ring compounds via charge transfer complexes. The oxidation of the cyclopropane derivatives (74) on illuminated ZnS or CdS has been studied. Irradiation of the cyclopropane (75) in pentane for 20 h yields the dimers (76, 35X) and (77, 15X). 

Change of solvent to benzene also yields these dimers which are accompanied by the adducts (78) and the furan (79). The adducts (78) are formed via a hydrogen abstraction pathway. The photochemical isomerization of the spirocyclopropane derivatives (80) affords the carbazole derivatives (81). This reaction involves ring-opening of a cyclopropyl bond followed by cyclization of the resultant biradical. An oxidative step must also be operative. 

The dihjrdro naphthalene (82) is photochemically reactive. Its irradiation in hexane at room temperature gives 2-methylnaphthalene and the methylidene naphthalene (83). Irradiation at -45 C follows a different path and yields the three new products (84). (85), and (86) as well as the methylidene naphthalene (83).  

1 The Di-7i-methane Rearrangement and Related Processes - Zimmerman and co-workers have reported results of calculations carried out on the well 

A reinvestigation of the photobehaviour of the triene (81) at 254 nm has identified two new products (82) and (83). The authors suggest that a carbene species is involved in the formation of the cyclopropene (83).  

Full details of the rearrangement of the vinylcyclopropene (87) have been published. This supplements a previous note. Electron transfer from 3,3 -dimethylbicyclopropenyl (88) to chloranil or fluoranil results in the formation of o -and m -xylene in a ratio of 4 1.  

The photochemical ring opening of cyclopropyl anions has been studied and found to be substitution dependent. Thus irradiation of (89a) fails to bring about ring opening while irradiation of (89b) affords the anion (90).  

This report supplements one already published. The synthetic 

A review has dealt with the di-x-methane type rearrangements of 

cjcyclo-octene to the triazole (91) by a photo Diels-Alder 

The results indicate that benzo-vinyl bridging at the carboxylate 

The ethenoanthracene (104) undergoes an acetone-sensitized di-ic-methane reaction to yield (105) and (106) in a ratio of 4 1. Direct irradiation also affords these products but in addition a different reaction path yields the new products (107) and (108). The formation of these products, which involves a chlorine 

Kaupp has published a review in which reference is made to the di-7r-methane reaction, a process which continues to yield interesting results. The di-Ti-methane J. Saltiel and D. W. Eaker, Chem. Phys. Lett., 1980, 75, 209. 

The acetone-sensitized irradiation of the bicyclo-octadienones (52) leads to the formation of a single photoproduct (53) in each case. This product is presumed to arise from a di-7c-methane reaction involving the bridging intermediate (54) exclusively, despite the polar substituents in the benzene ring. In constrast, similar irradiation of the compounds (55) leads to products, the nature of which is dependent upon the type and position of the polar substituent. The results are 

Kasahara, H. Sugiyama, and M. Nitta, Kokagaku Toronkai Koen Yoshishu, 1979,156 Chem. Abstr., 

Kuzuya, E. Mano, M. Ishikawa, T. Okuda, and H. Hart, Tetrahedron Lett.. 1981, 22. 161.3. 

Prolonged irradiation of the tricyclic olefin (63) affords the spiro-compound (64) as the sole product.However, on shorter exposure times this compound is accompanied by the isomeric material (65). It is clear from a separate study that the irradiation of this dihydronaphthalene results in its conversion into the starting material (63). This compound (63) is also formed on irradiation of the isomeric compound (64) and (66). Both the products (64, 65) from the initial irradiation result from the migrations of the methylene unit on a methylene indene unit. Theoretical aspects are discussed. 

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Other Reactions Involving Cyclopropane Rings. 2.2.1 SET Induced Reactions The radical cation of phenylcyclopropane can be obtained by irradiation in the presence of chloranil as the electron accepting sensitizer. ... 

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