Cycloaddition Reactions - Synthesis
Each of the molecules shown on the left can be prepared by a simple [4+2] cycloaddition reaction. For each compound, draw the structure of the diene and dienophile which would be required for the synthesis, paying particular attention to the stereochemistry of the reactants.Click the mouse on the molecule to view the answer;
click on the arrow for help in visualizing the cycloaddition.
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In a [4+2] cycloaddition reaction, new bonds will form between the terminal carbons of the diene and the alkene carbons of the dienophile, as shown below. In the cyclohexene ring, the substituents which were originally on the dienophile are trans- (1,2-diequatorial), therefore the starting dienophile must also have trans stereochemistry.
In a [4+2] cycloaddition reaction, new bonds will form between the terminal carbons of the diene and the alkene carbons of the dienophile, as shown below. In the cyclohexene ring, the substituents which were originally on the dienophile are cis- (1,2-axial-equatorial), therefore the starting dienophile must also have cis stereochemistry.
In a [4+2] cycloaddition reaction, new bonds will form between the terminal carbons of the diene and the alkene carbons of the dienophile. In the cyclohexene ring, the substituents which were originally on the dienophile are cis- (1,2-axial-equatorial), therefore the starting dienophile must also have cis stereochemistry. The methyl groups on the diene are trans (1,4-diequatorial), therefore the two double bonds in the diene must be cis-trans.
To identify the reactants in a [4+2] cycloaddition reaction, identify the carbons of the dienophile (they will be the two carbons in a six-member ring which are opposite to the double bond in the product) and mentally split the bonds, separating the carbon skeletons of the diene and the dienophile. In this problem, it is helpful to convert the chair cyclohexene into the boat conformation.
To identify the reactants in a [4+2] cycloaddition reaction, identify the carbons of the dienophile (they will be the two carbons in a six-member ring which are opposite to the double bond in the product) and mentally split the bonds, separating the carbon skeletons of the diene and the dienophile.
To identify the reactants in a [4+2] cycloaddition reaction, identify the carbons of the dienophile (they will be the two carbons in a six-member ring which are opposite to the double bond in the product) and mentally split the bonds, separating the carbon skeletons of the diene and the dienophile. In this problem, it is helpful to convert the chair cyclohexene into the boat conformation.
