Di ti methane rearrangement

Pokkuluri et al. have recently addressed the question of the directionality of free volume in their studies on the solid state di-Ti-methane rearrangement of methyl 2-benzoyl-l,4-dihydrol,4-ethenonaphthalene-3-carboxylate, 30 [150]. The title compound gives two different sets of products upon solution and solid state irradiation, both resulting from di-Ti-methane process involving 1,3-diradical intermediate (Scheme 14). Strikingly, the solid state products derive via less stable 1,3-diradical intermediates, 31 and 32 whereas the... 

The classical di-Ti-methane rearrangement can be considered as a 1,2 shift of one of the n units to the other followed or accompanied by ring closure to... 

Electrophilic dienes 457 and 459 can also be converted into electrophilic cyclopropanes 458 and 460 via a di-Ti-methane rearrangement as illustrated by the examples of equation 155 . The rearrangement of the dienes follows a typical di-7c-methane... 

Theoretical studies of reaction 25 and a portion of the di-Ti-methane rearrangement (equation 25a) suggested these processes have similar energetics even though the details of the transformations were found to be different ... 

Irradiation of the P,ri-unsaturated ketones, bicyclo[2.2.1]hept-5-en-2-one and bicyclo[2.2.2]oct-5-en-2-one included within MY zeolites promotes an oxa-di-Ti-methane rearrangement. The transformation is thought to occur by a triplet state which has its origin in the heavy cations present within the supercage. 

The Oxa-Di-n-methane reaction and Related Processes. Interestingly, some P,y-unsaturated ketones do not undergo 1,3-acyl shifts or the oxa-di-Ti-methane rearrangement. An example of this is compound (61), which on irradiation undergoes only a Norrish Type II hydrogen abstraction. ... 

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. 

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