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The Di-n-Methane Rearrangement

The latter reaction is an example of the di-n-methane rearrangement This rearrangement is a very general reaction for 1,4-dienes and other systems that have two n systems separated by an -hybridized earbon atom ... [Pg.776]

The photochemical isomerization of 1,4-dienes 1, bearing substituents at C-3, leads to vinyl-cyclopropanes 2, and is called the di-n-methane rearrangement This reaction produces possible substrates for the vinylcyclopropane rearrangement. [Pg.96]

Dienes carrying alkyl or aryl substituents on C-3 can be photochemically rearranged to vinylcyclopropanes in a reaction called the di-n-methane rearrange-... [Pg.1460]

Photochemistry of non-conjugated dienes 6. Other systems undergoing the di-n-methane rearrangement... [Pg.317]

Diarylcyclohex-2-enones undergo a different photorearrangement to bicydol3.1.0]hexan-2-ones, in which an aryl substituent migrates from C-4 to C-3 (4.641. This reaction finds a parallel in the di-n-methane rearrangement of 3-phenylalkenes (see p. 54). It is usually efficient (<> — 0.1-0.2), it occurs by way of the (n.Jt ) triplet... [Pg.132]

Direct irradiation of dibenzobarrelene (106a) in solution yields the di-T-methane product (107) and the cyclooctatetraene (108). Acetone-sensitized irradiation affords compound (107) only. In the crystalline phase, however, a new product (109) is obtained as well as (107) and (108). A reinvestigation of this has suggested that the biradical (110) is involved in the formation of both the ester (109) and the cyclooctatetraene (108). The formation of the biradical could involve a tri-m-methane intermediate such as (111). Other examples (106b, c) have been studied and while the solid state irradiation does not yield the appropriate diester corresponding to (109) the cyclooctatetraene obtained does have the correct substitution pattern in confirmation of the involvement of a biradical analogous to (110) rather than the (2+2)-cycloaddition reaction path which has been favoured in the past. A further study of the asymmetric induction in the di-n-methane rearrangement has examined the... [Pg.188]

The Di-n-Methane rearrangement provides an illustrative case and is of intrinsic interest relative to the two main reaction intermediates — diradical 1, and diradical 2. This... [Pg.11]

In a continuing studyevidence was adduced that diradicals 1 and 2 are energy minima and are nonequilibrating under the usual reaction conditions of the di-n-methane rearrangement. It also proved possible to identify a higher energy triplet diradical 1, that is, Tg. Two independent routes to and Tg were found experimentally. These were applied to dim-... [Pg.12]

In most of the acyclic examples of the di-n methane rearrangement studied, there has been methyl substitution on the central (C-3) atom. We should expect that electron-withdrawing substituents (relative to —CH3) on C-3 would lower the energy of the basis orbitals on C-3 and slow the transformation shown in the diagrams for schemes (3) and (4). [Pg.343]

Substitution at the central carbon C3 plays a crucial role in facilitating or inhibiting the second step of the di-n-methane rearrangement. The structure of CVCN would particularly favor the formation of a radical center at C3 in the... [Pg.24]

In distinction to the oxa-di-rr-methane rearrangement, the di-n-methane rearrangement occurs in both singlet and triplet excited state. [Pg.75]

As one would expect, the di-n-methane rearrangement is regiospecific in asymmetric cases, e.g.. [Pg.459]

When the central sp -carbon of 1,4-diene is unsubstituted, the di-n-methane rearrangement is less favorable. The reaction of l,l,5,5-tetraphenyl-2,4-dideuterio-l,4-pentadiene 50 illustrates the fact [46]. [Pg.230]

The rearrangement is analogous to the di-n-methane rearrangement and is considered as 1,2-shift of imino group from C(3) to C(4), followed by a o bond formation between C(3) and C(5). For example, the photorearrangement of P,y-unsaturated imine 55 gives cyclopropyl imine 56, which on hydrolysis gives cyclopropane aldehyde 57 [62]. [Pg.234]

The rearrangement is stereospecific with inversion of configuration at C(4). It is a photochemically allowed [jia + cjJ] cycloaddition process. The mechanism is very similar to the di-n-methane rearrangement. It involves 1,2-shift of C(5)-C(4) o bond to C(3) followed by formation of a new o bond between C(2) and C(4) using back lobe of C(4)-p-orbital. [Pg.252]

Zimmerman HE, Armesto D (1996) Synthetic aspects of the di-n-methane rearrangement, Chem Rev 96 3065... [Pg.272]

Zimmerman has chosen to describe the di-n-methane rearrangement as in Mobius array which corresponds to a delocalised transition structure for an allowed photochenucal reaction, but not for ground state reaction. [Pg.236]


See other pages where The Di-n-Methane Rearrangement is mentioned: [Pg.776]    [Pg.1647]    [Pg.1650]    [Pg.459]    [Pg.121]    [Pg.725]    [Pg.189]    [Pg.189]    [Pg.1692]    [Pg.501]    [Pg.501]    [Pg.24]    [Pg.352]    [Pg.356]    [Pg.227]    [Pg.227]    [Pg.227]    [Pg.664]   


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