Asymmetric Catalylysis Of Α-Diazoketones Lab Report
Asymmetric Catalysis in Intramolecular Reactions of α-Diazoketones.
Abstract:
Carbon-hydrogen insertion reactions involve the insertion of a carbene, a neutral carbon atom or molecule with two unpaired valence electrons, into an unactivated carbon-hydrogen bond. This reaction produces many commercially valuable compounds. The reaction itself involves the use of diazocarbonyl compounds which contain an N2 ligand on a carbon alpha to a carbonyl. The reaction is thermodynamically favourable as it involves the release of nitrogen gas. The carbon hydrogen bond is extremely strong and is difficult to break down; hence a catalyst, a substance which lowers the energy required for a reaction to occur, is required in order for the reaction to go to completion. …show more content…
Electrophilic addition causes N2 to be lost, which is a thermodynamically favourable process, resulting in the formation of a stable carbene. The carbene is the intermediate and in this reaction, it is a highly reactive, neutral molecule. The carbene acts as an electrophile and proceeds to react with carbon-carbon and carbon–hydrogen bonds. The final step in the process, involves the transfer of the carbene and regeneration of the metal catalyst, hence completing the catalytic cycle.
The electron density of the metal-carbenoid species plays a key role in determining the chemoselectivity, regioselectivity and stereoselectivity of the product. The level of electron density on the carbenoid is greatly influenced by the nature of the groups attached to the carbene (Figure 3): electron withdrawing acceptor groups act to decrease electron density, which increases reactivity, while electron donating donor groups serve to increase electron density which stabilises the structure and raises chemoselectivity.
Figure …show more content…
It was reported that when there was competition between a double bond and an O–H functional group of an unsaturated alcohol for a metal carbene, the O–H insertion product is favoured. The percentage yield as a ratio of ether: cyclopropanol was 81:19 when the ligand on the rhodium catalyst was a methyl group[7]. It was found that changing the ligand in the rhodium catalyst did not alter the reaction[14]. Another example of a X–H insertion reaction is the formation of β-Lactam rings from Rh(II) catalyzed N-H insertion reactions where yields of 76-85% were obtained[15].
3) The electrophilic carbene can carry out a diverse range of reactions including the formation of an ylide. An ylide is a compound where one atom contains a negative charge and another atom holds a positive charge. Both the positive and negative charges are contained on the same molecule. When an α-diazocarbonyl compound reacts with an aldehyde or ketone, the carbonyl acts as a nucleophile and will attack the electron-deficient carbene centre [7]. This will form an ylide. In the α-diazocarbonyl compound, the carbonyl carbon is negatively polarised due to the N2
Abstract:
Carbon-hydrogen insertion reactions involve the insertion of a carbene, a neutral carbon atom or molecule with two unpaired valence electrons, into an unactivated carbon-hydrogen bond. This reaction produces many commercially valuable compounds. The reaction itself involves the use of diazocarbonyl compounds which contain an N2 ligand on a carbon alpha to a carbonyl. The reaction is thermodynamically favourable as it involves the release of nitrogen gas. The carbon hydrogen bond is extremely strong and is difficult to break down; hence a catalyst, a substance which lowers the energy required for a reaction to occur, is required in order for the reaction to go to completion. …show more content…
Electrophilic addition causes N2 to be lost, which is a thermodynamically favourable process, resulting in the formation of a stable carbene. The carbene is the intermediate and in this reaction, it is a highly reactive, neutral molecule. The carbene acts as an electrophile and proceeds to react with carbon-carbon and carbon–hydrogen bonds. The final step in the process, involves the transfer of the carbene and regeneration of the metal catalyst, hence completing the catalytic cycle.
The electron density of the metal-carbenoid species plays a key role in determining the chemoselectivity, regioselectivity and stereoselectivity of the product. The level of electron density on the carbenoid is greatly influenced by the nature of the groups attached to the carbene (Figure 3): electron withdrawing acceptor groups act to decrease electron density, which increases reactivity, while electron donating donor groups serve to increase electron density which stabilises the structure and raises chemoselectivity.
Figure …show more content…
It was reported that when there was competition between a double bond and an O–H functional group of an unsaturated alcohol for a metal carbene, the O–H insertion product is favoured. The percentage yield as a ratio of ether: cyclopropanol was 81:19 when the ligand on the rhodium catalyst was a methyl group[7]. It was found that changing the ligand in the rhodium catalyst did not alter the reaction[14]. Another example of a X–H insertion reaction is the formation of β-Lactam rings from Rh(II) catalyzed N-H insertion reactions where yields of 76-85% were obtained[15].
3) The electrophilic carbene can carry out a diverse range of reactions including the formation of an ylide. An ylide is a compound where one atom contains a negative charge and another atom holds a positive charge. Both the positive and negative charges are contained on the same molecule. When an α-diazocarbonyl compound reacts with an aldehyde or ketone, the carbonyl acts as a nucleophile and will attack the electron-deficient carbene centre [7]. This will form an ylide. In the α-diazocarbonyl compound, the carbonyl carbon is negatively polarised due to the N2