Di-7i-methane rearrangements

It has been found that the di-7i-methane rearrangement can proceed through either a... 

The resistance of the unsubstituted system to the di-7i-methane rearrangement probably occurs at the second step of the rearrangement. If the central carbon is unsubstituted, this step results in the formation of a primary radical and would be energetically unfavorable. 

Direct irradiation of 2,5-dihydrofuran (175) results in the formation of furan, tetrahydrofuran, and the isomeric oxiran (176).146 Certain 2,5-dihydrothiophen derivatives are similarly converted to the corresponding vinylthiirans,147 whereas 5,5-diaryl-2,5-dihydrofurans are reported to undergo di-7i-methane rearrangement.148 An unexpected transannular phototransformation has been observed on irradiation of the l,3-dioxolen-2-one (177)... 

Synthetic aspects of the di-7i-methane rearrangement have been reviewed.273 An aryl version of the cyclopropyl-7i-methane rearrangement has been reported 274 see (226) —> (227). A model study of the mechanism of the di-7i-methane and lumiketone... 

For more than 30 years, di-7i-methane processes were limited to the three different types of (3,y-unsaturated systems mentioned above. However, recent studies have shown that the rearrangement is applicable to 2-aza-1,4-dienes [13]. Thus, triplet-sensitized irradiation of compound 11 affords the cyclopropylimine 12 and the TV-vinylaziridine 13 (Sch. 6). The photoreaction of 11 represents the first example of a 2-aza-di-7i-methane rearrangement (2-ADPM) that brings about the formation of a heterocyclic product. The reaction has been extended to other 2-azadienes that yield the corresponding cyclopropylimines regioselectively [13b]. 

For more than 30 years di-7i-methane rearrangements have stood as the paradigm reactions that occur in the excited state manifold exclusively. However, recent studies have shown that rearrangements of the di-7r-methane type can also occur in ground state of radical-cation and radical-anion... 

Di-7i-methane rearrangements of acyclic and monocyclic 1,4-dienes usually occur in the singlet excited state and, therefore, the reaction takes place on direct irradiation. This is an important limitation since nonconjugated alkenes absorb below 250 nm. Consequently, the DPM reaction in acyclic and monocyclic dienes is restricted to compounds in... 

Finally, the neoflavonoid latifolin, a major constituent of Daltergia latifolia, and its dimethyl and diethyl derivatives, undergo aryl-di-7i-methane rearrangements on both direct and triplet-sensitized irradiation [27d,e] Thus, Pyrex filtered irradiation of the dimethyl derivative 69 affords the -cyclopropane 70 in 90% yield (Sch. 26). 

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... 

However, some substrates, generally rigid bicyclic molecules, (e.g., barrelene, p. 152, which is converted to semi-bullvalene) give the di-7i-methane rearrangement only from triplet states. 

When photolyzed, 2,5-cyclohexadienones can undergo a number of different reactions, one of which is formally the same as the di-7i-methane rearrangement. In this reaction, photolysis of the substrate 166 gives the bicyclo[3.1.0]hexenone (171). Although the reaction is formally the same (note the conversion of 161 to 162... 

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

In contrast to acyclic 1,4-dienes, which rearrange to vinylcyclopropanes from the excited singlet state vide supra), cyclic 1,4-dienes usually undergo the di-7i-methane rearrangement from the triplet state.Bicyclo[3.1.0]hex-2-enes (2, n = 1) and bicyclo[4.1.0]hept-2-enes (2, n = 2) are thus obtained from eyelohexa-1,4-dienes and eyclohepta-1,4-dienes, respectively. 

The synthetically most useful applications of the oxa-di-7i-methane rearrangement involve 2,5-bridged cyclohex-3-enones and cyclohept-3-enones or molecules eontaining such structural moieties. 

Ratio (ZiE) 75 25. Both products are apparently derived via a singlet carbene acid-catalyzed ring opening gave only the major isomer. Possibly via a di-7i-methane rearrangement via a spiropentane diradical. 

Keywords 1,4-pentadiene derivatives, 2-cyclohexenone derivatives, di-7i-methane rearrangement, photoirradiation... 

Latifolin (10), the major constituent of Dalbergia latifolia, gives trans-l-(5-hydroxy-2,4-dimethoxyphenyl)-2-(2-hydroxyphenyl)cyclopropane (11) as the sole di-7i-methane rearrangement product on irradiation in benzene.43... 

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