Don't worry about Stereochemistry

Chemistry Level 3

In 2004 a compound with the formula C X 15 H X 16 O X 6 \ce{C_{15}H_{16}O_{6}} was isolated form the aerial parts of Coriaria nepalensis , an important component in Chinese herbal medicine. It was named Corianlactone . The following scheme looks into the synthesis of a mixture of Corianlactone and its diastereomers:

We start with 2-Iodo 5-methylfuran and the above compound. Key steps are cycloadditons

  • They react in presence of Palladium(II) acetate to form A
  • Compound A reacts with the intermediate whose formula is C X 19 H X 17 P \ce{C_{19}H_{17}P} (that is formed from Triphenylphosphine) to form compound B
  • B reacts with H g C l X 2 \ce{HgCl_{2}} to form C whose formula is C X 13 H X 15 O X 2 C l \ce{C_{13}H_{15}O_{2}Cl}
  • C is mildly heated in presence of a base to form a compound D
  • D reacts with C X 2 H X 6 S X 2 \ce{C_{2}H_{6}S_{2}} in presence of Iodine and Methyl Chloride to form a E whose formula is C X 15 H X 18 O S X 2 \ce{C_{15}H_{18}OS_{2}}
  • E is heated in presence of an intermediate that is formed when acetyl chloride is heated with a base to give us F
  • F reacts with an excess of Meta Chloro Per Benzoic Acid and the resultant compound then reacts with H g C l X 2 \ce{HgCl_{2}} to give us the required mixture.

What is the number of rings in compound D ?

4 3 2 1

Vitthal Yellambalse by Vitthal Yellambalse , 22, India

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1 solution

We start from C whose chemical formula is known to us. The reaction of B to C is a simple dithiane removal and A to B is a Wittig reaction involving Triphenyl methyl phosphonium ylide (this is deduced from the formula). This tells us that the A possesses a chemical formula C 14 H 17 O 2 S 2 C l C_{14}H_{17}O_{2}S_{2}Cl implying a coupling reaction must occur :

The structures of C and B are easily found after this :

We now shift our focus to E which can be thought of as a dithiane protected D . Knowing this, compound D 's chemical formula is found to be C 13 H 14 O 2 C_{13}H_{14}O_{2} . Now it becomes apparent that during the conversion of C to D that a loss of H C l HCl must occur. The reaction conditions support a cyclo-addition between the furan ring and the de-hydrochlorinated moiety.

The heating of acetyl chloride in presence of a base generates a ketene that reacts with E to form F :

The next set of reactions are the Baeyer-villager oxidation and Epoxidation, followed by dithiane removal to generate a racemic mixture containing Corianlactone :

D contains two five membered rings and one six membered ring and hence the answer is 3 \boxed{3}

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