Rearrangements di-n-methane

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 ... 

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. 

A related reaction is the oxa-di-n-methane rearrangement, where one of the C=C double bonds is replaced by a C=0 double bond. The substrates are thus /3,y-unsaturated ketones. The rearrangement proceeds from the triplet state. This oxa-variant gives access to highly strained molecules containing small rings, as has been demonstrated by irradiation of norborn-5-ene-2-one 10 ... 

Apart from the carbene-1,2-addition route starting from 1,3-dienes, vinylcyclo-propanes may be obtained from 1,4-dienes through a di-n-methane rearrangement. 

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

Hixson<27) prepared the deuterio compound (31) and found that photolysis produced only compound (32) resulting from a di-n--methane rearrangement and not from a hydrogen migration ... 

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

Direct irradiation of the (CH)10 hydrocarbon triquinacene (26) in pentane solution gave five different (CH)10 isomers along with some naphthaline and azulene. The two major products were pentacyclo[4.4.0.02 4.03 i0.05,9]dec-7-ene (27), arising from an intramolecular [2 + 2] cycloaddition, and hexacyclo[4.4.0.02,4.03,10.05,8.07 9]decane ( barettane , 28), which is formed via a di-n-methane rearrangement (see Section l.A.2.2.) followed by an intramolecular [2 + 2] cycloaddition,50... 

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... 

The tricyclic compound shown in the following scheme underwent a 1,2-acyl shift (oxa-di-n-methane rearrangement) to form the tetracyclic compound upon irradiation in a Pyrex immersion well in degassed dry acetone as both a solvent as well as a sensitizer. On the... 

In a series of papers, Zandomeneghi, Cavazza and coworkers [67,83] investigate the photo induced double (oxa)-di-n-methane rearrangement of a bicylcic ketone structure 22. 

The hetera-substituted di-n-methane rearrangement is currently an active area of investigation. So far, most examples have been reported for oxa and aza substitution. From the available data, it appears that the rearrangement is operative only when the heteroatom is in the 1-position. Replacement of the sfP-carbon at the 2-position or the spi carbon at the 3-position by heteroatoms such as O, N, S, Se, B, P, etc. entails systems which have not been investigated or which have proved incapable of giving di-n-meth-ane products. 

The + 2al or [,2 + Jl ] mode has the same stereochemical consequences. However, this mechanism, which does not involve the n bond between C-l and C-2, was excluded because no di-.n -methane rearrangement is observed upon irradiation of compound 122, which contains only one double bond. 

Me) cyclizes efficiently to give only (43, R = Ts, = Me) in 75% yield. In competition with this cyclization mode the aza-di-n-methane process occurs to yield the cyclopropanes (44) as shown in Scheme 3. Remarkably, the hydrazone derivatives (45) only undergo the aza-di-n-methane rearrangement to yield (46) efficiently. 

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