Organic Eriksen Flashcards
What equation do we use to figure out how many unsaturated bonds? (DBE)
DBE = 2x (No. C) + 2 - (No. H) / 2
why Syntesise complex molecules?
Structure determination, To prove the structure, the compound
were synthesised and it’s physical and chemical properties were
compared to the natural compound
Develop new chemistry.
Access to valuable chemicals, to gain access to valuable chemicals such as drugs and natural products in low abundance. A classic example of this is Taxol used in cancer treatment
Disconnections are done close to functional groups
Why synthesise tropinone?
The desire to synthesise tropinone in the early 1900’s was partly
to develop new chemistry but also to gain access to large quanti-
ties of tropinone. It was believed that tropinone could be used to
synthesise verious other important alkaloids based on the tropane
skeleton. It was also a way to verify the structure of the tropinone
formed in the degradation experiments of atropine.
How do we go about planning a synthesis of a complex molecule?
few options..
Reaction spotting: By recognising structural patterns and certain
atomic arrangements.
Retorsynthetic analysis: This is a formalised way of breaking down,
disconnecting, a molecule into fragment pairs that are nucle-
ophilic and electrophilic
Willstätter’s synthesis of tropinone (1901)
It was a 20 step linear synthesis with a total yield of 0.75%.
Willstätter saw a resemblance between tropinone and cyclohep-
anone
Robinson’s synthesis of tropinone (1917).
Robert Robinson had a completely different view compared to
Willstätter on the construction of tropinone. Robinson saw the con-
nection between tropinone and the Mannich reaction
mannich reaction lead to a remarkable two step synthesis of tropinone
in 89% yield
Chosing the “best” route.
Low cost: uses cheap starting materials or reagents?
Highest yield:
Safety concerns: avoid unnecessarily toxic or explosive reagents?
Environmental concerns: avoids toxic heavy metals such as chromium
sensible choice of starting material usually have 6–8 carbon atoms and 1–2 functional groups.
How do you calculate the overall yield?
calculate the yield for each individual reaction and
then multiply all the yields together
What is the Linear strategy for total synthesis ?
using the product from the previous step in the next reaction until the target molecule
What is the Covergent strategy for total synthesis ?
convergent strategy have two or more starting points and forms fragments that are connected together (fragment D and F in figure 4b)
Linear synthesis of Viagra.
The synthesis of Viagra is a good example of a synthesis that was
originally developed as a linear synthesis and later was converted
to a convergent synthesis.
In total the yield for the linear synthesis of Viagra is(0.62 ×0.71 ×
0.42 ×0.88 ×0.71 ×0.88) ×100 = 10%.
The perfect protecting group. 5
