The reaction between aldehyde 1 and ketone 2 at room temperature yields aldol 3

Question

The reaction between aldehyde 1 and ketone 2 at room temperature yields aldol 3 in 85% yield. If the reaction mixture is heated at reflux, then the alpha, beta- unsaturated ketone 4 is the major product. 4 is really a mixture of Z and E isomers: compounds 5 and 6. a) Label 5 and 6 as to whether they are E or Z. b) Using the Newman projection spheres shown below, and looking down the C_3-C_4 bond with C_3 in front, draw the gauche conformers which lead directly to the E and Z isomers. (Use the abbreviation LG for the carbon 5 group.) Draw a 3^rd gauche conformer which does not lead to the loss of water, c) Use equilibrium arrows to indicate the energy relationship between all three of these conformers. Name compounds 3 and 6 from question 8. For compound 3 only, ignore stereochemistry.

Explanation / Answer

8.(a): 5 is Z isomer, and 6 is E isomer.

9: Compound-3: 1,1,1 - trifluoro-4-hydroxy-5-methyl-5-phenylheptan-2-one.

Compound-6: (3E, 5R)-1,1,1 - trifluoro-5-methyl-5-phenylheptan-3-en-2-one.

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