REACTIONS IN ORGANIC CHEMISTRY

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In 1899, Wagner and Brickner observed a regrouping when treating a-pinene with hydrochloric acid. This observation contradicted the classical theory that was based on the invariance of the skeleton of the molecule.
In 1922, H. Meerwein established a cationic mechanism that explained the reaction. This mechanism occurs with the formation of a carbocation that undergoes a [1,2] rearrangement of hydrogen, alkyl or aryl groups.
wagner meerwein regrouping 01

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The Wacker oxidation allows the transformation of alkenes into the corresponding ketones by treatment with Pd in the presence of copper salts. Copper has the ability to oxidize palladium(0) to palladium(II), the latter being the catalytic agent in the reaction.

wacker oxidation 01

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In 1981, Weinreb and Nahm obtained ketones by adding lithium or magnesium organometallics to N-methyl-N-methoxyamides.
Weinreb's amides are prepared from acid halides or anhydrides by reaction with N,O-dimethylhydroxylamine in the presence of base (pyridine).
 
weinreb synthesis 01
weinreb synthesis 02

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In 1902, Wolff observed that treating diazoacetophenone (α-diazoketone) with Ag2O/H2O produced a rearrangement that generated phenylacetic acid.

wolff regrouping 01

By replacing water with ammonia, phenylacetamide is obtained.

wolff regrouping 02

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The reduction of aldehydes and ketones to alkanes via the corresponding hydrazone or semicarbazone under basic conditions and strong heating is called the Wolff-Kishner reduction.
The reaction is carried out in solvents with high boiling points 180-200°C (ethylene glycol). Substrates with ester and amide groups are hydrolyzed to the corresponding acids. Strongly hindered carbonyls are reduced more slowly. In the case of a,b-unsaturates, hydrazine condenses to give pyrazolidines.
 
wolff kishner 01

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In 1855, Wurtz treated alkyl halides with sodium metal to obtain the corresponding symmetrical alkane. The coupling of two sp 3 carbons belonging to alkyl or aryl halides by treatment with sodium metal is known as Wurtz synthesis. On the other hand, the coupling of an alkyl halide with an aryl halide is called a Wurtz-Fittig reaction.
 
1. Homocoupling of bromoethane to yield butane
 
wurtz coupling 01

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In 1979, Yamaguchi et al. developed a procedure to obtain esters and lactones under mild conditions through alcoholysis of the corresponding mixed anhydride.
The formation of a lactone starts from the treatment of the hydroxy acid with 2,4,6-trichlorobenzoyl chloride in the presence of triethylamine, necessary to neutralize the hydrochloric acid released at this stage. The mixed anhydride produced is treated with DMAP in toluene, under high dilution conditions, yielding the desired lactone.
 
yamguchi 01

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The Wharton fragmentation is a concerted reaction in which a leaving group is located in position 4 with respect to an electron donating group. The transfer of the free pairs of the donor group produces the fragmentation of the neighboring bond and the loss of the leaving group with the formation of double bonds. Let's see an example:

wharton fragmentation 01

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The Wharton synthesis allows α,β-epoxyketones to be transformed into allylic alcohols by treatment with hydrazine in acetic acid medium or hydrazine hydrate followed by strong base. The $\alpha,\beta$-epoxyketone is obtained from the $\alpha,\beta$-unsaturated ketone by oxidation with hydrogen peroxide in a basic medium.

wharton synthesis 01

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The Chugaev reaction allows the formation of olefins from xanthans.

reaction chugaev 01

It is a pyrolysis reaction that is generally carried out in the temperature range between 100 and 250ºC.

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Aldehydes, without alpha hydrogens, give the Cannizzaro reaction on treatment with a strong base (NaOH)

cannizzaro

In this reaction one molecule is reduced to alcohol, while the other is oxidized to carboxylic acid.

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The Blanc reaction allows the chloromethylation of aromatic compounds.

white reaction 01

It uses as reagents methane with gaseous hydrogen chloride in the presence of a Lewis acid. The result is the introduction of a hydroxymethyl group on the aromatic ring (benzene) whose hydroxyl is replaced by chlorine in the presence of hydrogen chloride.

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The Beckmann reaction produces the rearrangement of an oxime into an amide. This reaction is carried out in an acid medium.

beckmann transposition 01

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In 1989, G. Bartoli described the reaction of substituted nitroarenes with Grignard vinyl organometallics at low temperature, yielding substituted indoles after aqueous work-up. Three equivalents of magnesium are necessary, added to a cold nitroarene solution, which is stirred for twenty minutes, followed by the addition of saturated ammonium chloride solution and final extraction with ether. Better performance is obtained with indoles substituted in the ortho position to the nitro.
 
batoli indole synthesis 01
 

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The Barbier reaction makes it possible to obtain unstable organometallic reagents in the reaction medium. Initially it was carried out with Magnesium metal, generating magnesium in situ. Later it was extended to other metals: Sn, Zn..., being able to work in aqueous media, without requiring the protection of acid groups (hydroxyls).

babier reaction 01

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The Schiemann reaction consists of the thermal decomposition of aromatic diazonium tetrafluoroborates to yield the corresponding fluorinated derivative. Although diazonium salts are intestable, diazonium tetrafluoroborates have significant stability and can be prepared in good yield. Diazonium tetrafluoroborate is prepared from aromatic amines by the diazotization reaction.

Balz Shiemann 01

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The Baker-Venkataraman rearrangement transforms aromatic ortho-acyloxyketones to beta-diketones by basic treatment (catalysis). Beta-diketones are of great interest in the synthesis of chromones, flavones and coumarins. The most commonly used bases in the reaction are: KOH, potassium tert-butoxide, sodium in toluene, potassium hydride.

baker venkataraman 01

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1,5-Dienes isomerize by sigmatropic-[3,3] rearrangements on heating. Reaction known as Cope rearrangement. The rearrangement of N-substituted 1,5-dienes is called an aza-Cope rearrangement. Depending on the position occupied by nitrogen we have: 1-aza-, 2-aza-, 3-aza-Cope. The 3-aza-Cope regrouping coincides with the aza-Claisen.

aza cope 01

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Sigmatropic [3,3] rearrangements of N-allyleneamines are known as aza-Claisen rearrangements. This reaction is analogous to the Claisen rearrangement of allyl vinyl ethers.

aza claisen 01

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Reaction analogous to the Wittig rearrangement, in which alpha metal ethers rearrange alkoxides, generating secondary or tertiary alcohols after hydrolysis. In the case of aza-[2,3]-Wittig, these are alpha metallated allylic tertiary amines which produce secondary amines after hydrolysis.

aza23wittig 01