The spicy flavor of cayenne pepper is due mainly to a compound called capsaicin.

Question

The spicy flavor of cayenne pepper is due mainly to a compound called capsaicin. Its laboratory synthesis is given below. Draw the structures of compounds A - D, as well as the structure of Capsaicin. I am curious to know whether you think that having a Final Exam for the laboratory portion of Organic Chemistry II was a valuable exercise. Please share your thoughts on the matter, CHE 224A students should express their thoughts on the most memorable organic lab experiment they did at their home institution.

Explanation / Answer

1. CH3-CH(CH3)-CH=CH-CH2-CH2-CH2Br + PBr3 -----------> CH3-CH(CH3)-CH=CH-CH2-CH2-CH2Br or C8H15Br

(2-methyl-3-hepten-1-ol)    (2-methyl-3-hepten-1-bromo or A)

2. CH3-CH(CH3)-CH=CH-CH2-CH2-CH2Br +  NaCH(CO2CH2CH3)2 ------------> CH3-CH(CH3)-CH=CH-CH2-CH2-CH2CH(CO2CH2CH3)2 + KOH, H2O, heat ------------> CH3-CH(CH3)-CH=CH-CH2-CH2-CH2-CH2COOH + H3O+

---------------> CH3-CH(CH3)-CH=CH-CH2-CH2-CH2-CH(COOH)2 or B (C11H18O4)

3. CH3-CH(CH3)-CH=CH-CH2-CH2-CH2-CH(COOH)2 after hheating at 160-1800C -------> CH3-CH(CH3)-CH=CH-CH2-CH2-CH2-CH2-COOH or C (C10H18O2)

4.  CH3-CH(CH3)-CH=CH-CH2-CH2-CH2-CH2-COOH + SOCl2 -----> CH3-CH(CH3)-CH=CH-CH2-CH2-CH2-CH2-COCl or D (C10H17ClO)

5. CH3-CH(CH3)-CH=CH-CH2-CH2-CH2-CH2-COCl -----------> CH3-CH(CH3)-CH=CH-CH2-CH2-CH2-CH2-CONHCH2-C6H3-(OH)(OCH3) or E (C18H27NO3) i.e. Capsaicin

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