Edited Invalid date
16 -- Part 7: AROMATIC COMPOUNDS
There is a chance that the ring has no strong electron-drawing groups.
It needs a powerful base or high temperatures.
A carbanion is given by deprotonation adjacent to the leaving group.
The leaving group is expelled by the carbanion.
The product is given by reprotonation.
Show the expected products of the following reactions.
The benzyne mechanism is likely if stronger conditions are required.
The triple bond of benzyne is very strong.
Predict the product of the Diels-Alder reaction of benzyne.
Many useful drugs, fabrics, and plastics require the synthesis of aromatic rings with alkyl, aryl, or vinyl groups attached in the presence of multiple types of functional groups.
To avoid these limitations, organic chemists have developed a wide variety of methods that tolerate many other functional groups.
Some of the most successfulcoupling reactions use transition metals that change valences easily, adding and eliminating substituents as they pass from one oxidation state to another.
Aryl and vinyl halides are used to make substituted benzenes and alkenes.
There are many new methods using other transition metals in the reagents and catalysts.
Most of the reactions substitute organic groups for halogen atoms.
First, we consider the use of organocuprates to couple with aromatic rings and alkenes, and then look at palladium-catalyzed reactions that form substituted aromatic rings.
The reaction of two equivalents of an organolithium reagent with cuprous iodide creates the lithium dialkylcuprate reagents.
A new carbon-carbon bond is formed when the dialkylcuprate is reacted with an alkyl, aryl, or vinyl halide.
The mechanisms of organocuprate reactions are not well understood.
Both vinyl and aryl halides can't undergo SN2 displacement.
There is a wide variety of com pounds that can be made by organocuprate reactions.
An aromatic ring can be found in either the aryl halide or dialkylcuprate reagent.
Iodides, bromides, and chlorides can be used as the halides.
The stereochemistry of the vinyl halide is preserved with an aryl cuprate.
Acyl halide with organocuprate gives a ketone.
The less substituted end of the alkene has a C bond.
The alkene and the bromide are usually monosubstituted.
The catalyst may be Pd(OAc)2 or PdCl2 or a variety of other compounds.
A small amount of catalyst is needed.
The HX released in the reaction is mitigated by adding a base such as triethylamine.
Many reactions use triphenylphosphine to complex with the palladium, which helps strengthen it and enhances its reactivity.
In drug synthesis, where the palladium catalysts can be recovered and recycled, the Heck reaction and its variant are used frequently.
Water can be used as the solvent in some Heck reactions.
The examples show the wide utility of the reaction.
A nitrile with a vinyl halide.
The Suzuki reaction is a substitution of an aryl or vinyl halide with an alkyl, alkenyl, or aryl boronic acid.
A wide variety of required heavy metals and other toxic functional groups can be found in these types of couplings.
B(OH) spent reagents.
R'B(OR)2 by-products are less hazardous and easier to dispose of.
The Suzukicoupling can use water as a solvent.
Water based Suzuki reactions are attractive for both industrial processes and labs that want to minimize the purchase and disposal of toxic solvents.
There are many combinations that can be coupled using Suzuki reactions.
The stereochemistry of the reagents is preserved by a vinyl halide with an alkenylboronate ester.
An aryl halide with arylboronic acid is used as a solvent.
Water and palladium are used as a solvent and catalyst in the synthesis of the anti-Inflammatory drug flurbiprofen.
alkyl-, vinyl-, and arylboronic acids can be used to make the boronate esters.
The hydroboration of double and triple bonds is similar to that of alkenes and alkynes in Chapters 8 and 9.
The less substituted end of a double or triple bond is usually added by the boron atom.
The B and H add the same side of a triple bond to give a trans alkenylboronate ester.
Adding a trialkyl borate allows the organolithium compound to form a carbon-boron bond and expel an alkoxide group.
View flashcards and assignments made for the note
Getting your flashcards
Privacy & Terms