Mar Gómez Gallego

A new photochemical synthesis of cyclopropanecarboxylic acids present in pyrethroids by the aza-di-π-methane rearrangement

Abstract A novel synthetic route to chrysanthemic acid, 2-cyclopentylidenmethyl-3,3-dimethylcyclopropanecarboxylic acid, fluorenespiro-2,2-dimethylcyclopropanecarboxylic acid and indenespiro-2,2-dimethylcyclopropanecarboxylic acid, all of them present in pyrethroids of known insecticidal activity, is described. The key step in the synthesis is the aza-di-n-rnethane rearrangement of some 1-aza-1,4,6-trienes and some 1-aza-1,4-dienes, using triplet sensitization.

Steric and electronic effects on the photochemical reactivity of oxime acetates of β,γ-unsaturated aldehydes

A general synthesis of 5-substituted N-acetoxy 3,3-dimethyl-1-azapenta-1,4-dienes starting from 2-(1,3-dithian-2-yl)-2-methylpropanal is described. The influence of 5-phenyl, 4-phenyl, 5-cyclohexyl, 5-tert-butoxycarbonyl and 5,5-dicyclohexyl substitution on the outcome of the photochemical reactions of the oxime acetates of β, γ-unsaturated aldehydes has been studied with a view to proving or disproving the operation of a deactivating free rotor in the aza-di-π-methane rearrangement. The results obtained show that if the radical formed at C-5 can be stabilized by conjugation with an aryl group or by certain types of disubstitution then the aza-di-π-methane rearrangement takes place successfully. In any other situation the reaction fails. These results clearly show that the free rotor effect is not responsible for the failure of C-5 monosubstituted 1-aza-1,4-dienes to undergo the aza-di-π-methane rearrangement.

Unexpected reactivity of the anion derived from benzophenone benzoylhydrazone in the presence of electrophiles

Abstract The reactions of the anion of benzophenone benzoylhydrazone with acid chlorides are described. These afford dihydro-oxadiazoles. In the absence of acid chlorides the anion from the benzoylhydrazone yields open chain products such as enol ethers and N-methyl amides. An electron transfer mechanism is proposed to account for this change in behaviour.

Unexpected influence of mono-phenyl substitution on the photochemistry of β,γ-unsaturated oxime acetates

On irradiation the oxime acetate of trans-2,2-dimethyl-4-phenylbut-3-enal (5) undergoes stereospecific aza-di-π-methane rearrangement to the oxime acetate of trans-2,2-dimethyl-3-phenylcyclopropanecarbaldehyde (7), while surprisingly the irradiation of the oxime acetate of 2,2-dimethyl-3-phenylbut-3-enal (10) follows a different reaction path and affords the oxime acetate of 4-methyl-3-phenylpent-3-enal (13) by a novel 1,3-migration pathway.

The photochemical 1,5-benzoyl migration in 2,2-diaryl-1,4,4-triphenyl-3-azabut-3-en-1-ones. A novel rearrangement in β,γ-unsaturated enone systems

The synthesis of 2,2-diphenyl- and 2,2-bis(p-chlorophenyl)-1,4,4-triphenyl-3-azabut-3-en-1-one is described. The photochemical reactivity of these compounds is described and interpreted in terms of 1,5-benzoyl migration, the terminus of which rearrangement is a phenyl ring. This type of reactivity is novel for β,γ-unsaturated systems.

The photochemical rearrangement of 3-aza-1,2,2,4,4-pentaphenylbut-3-en-1-one. A novel reaction in a β, γ-unsaturated enone.

Abstract Irradiation of 3-aza-1,2,2,4,4-pentapheynylbut-3-en-1-one in t-butanol gives two photoproducts in good yield. The formation of these products is interpreted in terms of 1,3- or 1,5-benzoyl migration. This is the first reportof an acyl migration from a saturated carbon into a substituent phenyl group.

A study on the scope of the photochemical 1,3-migration of oximino groups in β,γ-unsaturated oximes and oxime derivatives

While the aza-di-π-methane rearrangement is the normal photoreactive behaviour of β,γ-unsaturated imines and oxime acetates, the results obtained in this study show that 1,3-migrations of acetoxyimino groups in β,γ-unsaturated oxime acetates takes place only when all the parameters are correct. The rearrangement takes place when there is a quaternary carbon separating the two π-systems and when one of the radical centres in the intermediate cyclobutyl 1,4-biradical is stabilized by conjugation with a phenyl ring. Suppression of the free rotor effect also helps to promote the reaction. These criteria are fulfilled in compounds 1a and 7a. The reaction was extended to the β,γ-unsaturated oximes l b and 7b where again the 1,3-migration of the oximino group took place.

Photochemical synthesis of quinoline derivatives by cyclization of 4-aryl-N-benzoyloxy-2,3-diphenyl-1-azabuta-1,3-dienes

The synthesis and the photochemical reactions of a series of 4-aryl-N-benzoyloxy-2,3-diphenyl-1-azabuta-1,3-dienes are described. The photochemical cyclization affords good yields of 2,3-diphenylquinoline derivatives.

Level 3 - Case 38 Substitution of β-Halostyrenes by MeS-

β-Bromostyrenes 1 react rapidly with MeS- or i-PrS- in HMPA, at room temperature, to give the vinylic substitution products 2 with high yields (> 95%) and almost complete retention of the configuration (> 98%) (Scheme 38.1).

Level 1 — Case 5 Rearrangements from Tetrahydropyran Derivatives

When tetrahydropyranyl ethers 1 and 2 are exposed to excess (3.6 equiv) of SnCl4 at low temperature, an oxygen to carbon rearrangement occurs, resulting in several distinct products that are obtained as diastereomeric mixtures (Scheme 5.1). The formation of these products could be rationalized by considering the initial generation of a carbocationic intermediate (3 or 4) from which different final products can be obtained. For example, trapping of cation 3 by chloride ion (already present in the medium) yields the chlorohydrins 5, whereas aldehydes 6 would be obtained from a 1,2-hydride shift in the intermediate 3. In other cases, as in 4, the cation and the oxygen bearing the Lewis acid (still sufficiently nucleophilic) are placed at a distance that allows the cyclization faster than the other competing pathways, leading to bicyclic compounds like 7.