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Modern Organic Chemistry

exam

09-04-2015

time: 3 hours

Every answer sheet must be provided with yourname, study and student number

(The maximum number of points for every question isindicated)

Question 1. (16 points)The group of Danishefsky presented a route of synthesisto mamanuthaquinone, part of which is presented in thescheme below.

a) Provide the structure of product 2 and the mechanismof the corresponding reaction.b) Provide the structure of product 3 and the mechanismof the corresponding reaction.c) Provide the structure of product 4 and the mechanismof the corresponding reaction.d) Provide the mechanism of the conversion of 4 ~S.Explain the stereochemistry of the reaction.

Question 2. (16 points)In the synthesis to capnellene by the group of Shibasakithe following transformations were executed.

---------------------.o :Bz="t,~i

r V:I--------------------~

(C4HgbSnH

NC1-N=N-fCN

Zn/Cu

8

1 NaOH

9

1 a) Give the reaction conditions and the structures of the -corresponding intermediates, which can be used toconvert 6 into 7.b) Give the structure of compound 8 and the mechanismof the corresponding reaction. Explain thestereochemistry of the reaction .

..c) Give the structure of compound 9 and the mechanismof the corresponding reaction .

. d) Provide the mechanism of the conversion of 9 -+ 10.

Question 3. (14 points)A new structure of the fungal metabolite, mycosporulonehas been proposed on the basis of a tota I synthesis.

H+,toluene,refluxremoval H20.. 15

o

The first step of the synthesis comprised thecondensation of ethyl 4-oxo-2-pentenoate 11 andpropionaldehyde 12 employing pyrrolidine 13 as anorganocatalyst to give 14. Crude 14 was subjected tostandard Dean-Stark dehydration conditions to afford 15as a mixture of diastereomers.a) Provide the structure of compound 14 and themechanism of the corresponding reaction.

Q b) Provide the structure of compound 15 and themechanism of the corresponding reaction.c) Provide the mechanism of the conversion of 15 -+16.

Question 4. (28 points)Ecklonialactone A is an oxylipinalgae Ecklonia stolonifera.

~ 0

isolated from the brown

NaH and then o-0-,S-CI1 eq - 11

o .19

~II lIl/OH

BnO/ 17 OH

OBn20

AeO OAe"

~

1-OAeI '0

·'1'1 .#'I/OTBS

22 0OH • 23 ---- •.•. 24 -----... 25

a) Give the structure of 18, including thestereochemistry and the mechanism of the conversion of17 -+ 18.b) Give the structure of 19, including thestereochemistry and the mechanism of the conversion of18 -+ 19.

• c) Give the structure, including the stereochemistry of20 and the mechanism of the conversion of 19 -+20.d) Give the mechanism of the conversion of 20 -+21.e) Give the structure of 23 and the mechanism of theconversion of 22 -+23.f) Give the structure of 24 and the mechanism of theconversion of 23 -+24.

11 g) Give the structure of 25 and the mechanism of theconversion of 24 -+ 25

Question 5. (16 points)The following reactions are used in the total synthesis ofFD-891 and mesembrane, respectively.

HOHO

HÖ 26

OBn

+ ,o~aBn

I 27

HO

I, ".'<,\\\"

Zn CH3~CH3

---- .•.~ 31___ --...~ 30

osn C2H50H reflux

o + ------~. 34

H

( a) Compound 28 is prepared in two steps from 26 and27. Describe the corresponding mechanisms, includingthe stereochem istry.

"\b) Give the structure of compound 30 and themechanism of 29 ~ 30.

're) Give the structure of compound 31 and themechanism of 30 ~ 31.

I d) Give the structure of compound 34 and themechanism of the conversion 32+33 ~ 34.

Question 6. (10 points)The scheme below shows two well-known reactions.

-\-035 Li

IN

(CH3bSi /" <,Si(Meb------ ..•~ 37

+/

THF/C}=O\

40

a) Provide the structure of compound 37 and themechanism of the corresponding reaction.b) Provide the structure of compound 40 and themechanism of the corresponding reaction. Explain thestereoehem istry of the reaction.