Photocyclization cyclopropanes

Park et al. [10] have recently reported an efficient photocyclization of 1-benzoyl-l-(o-ethylphenyl) cyclopropane (29) to the corresponding indanol 31. In this ketone, the cyclopropane ring bulk appears to be equivalent to that of two methyl groups, and forces the geometry of the 1,5-biradical intermediate suitable for cydization (Scheme 8.8). 

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... 

The monocyclic triene (288) is the initial photoproduct from irradiation of the diene (289) in methanol. However, this triene is not isolated but undergoes reaction with the solvent to yield the methanol adduct (290a, 35%), in Scheme 5, and the isomer (291, 12%) produced by the route shown in Scheme 6. Irradiation of (289) in methylene chloride follows a different path via intermediate (292), formed by photocyclization of (288) cyclopropane ring opening... 

The photocyclization reaction of 2-allylanilines, depending on the degree of alkylation at the N atom, has long been a subject of interest. When iV,iV-dialkylanilines 60a-62a were irradiated in methanol, the corresponding 2-cyclopropylanilines 60b-62b were formed in 73, 60 and 47% yield, respectively (equation 17)163. This reaction proceeds in the triplet state via a clean aromatic di-jr -methane rearrangement. However, no reaction occurs when 2-allyl-l-(Ai,Ai-dimethylamino)naphthalene is irradiated in methanol. Thus, this photochemical cyclopropanization of allylated anilines appears to have only a limited scope as preparative method, because it is successful only for a few substrates. 

Three- and Four-membered Rings. Methyl chrysanthemate (75) has been obtained as a 1 2 mixture of cis- and trans-isomers by the di-ir-methane cyclization of the diene ester (74) (Scheme 24). Cyclopropanes may also be prepared by the photocyclization of allylmagnesium bromide. ... 

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