CHEM3118 and CHEM3918 Synthetic Chemistry – Synthesis Assignment
Synthetic Chemistry
CHEM3118 and CHEM3918 Synthetic Chemistry – Synthesis Assignment
This assignment is marked out of 20 marks in total and makes up 12% of your final grade for the unit.
Submission: 11:59 pm, Sunday 7th May (Week 10) – upload to Canvas site as a single PDF file.
Synthetic chemistry requires us to be familiar with a wide and diverse set of chemical reactions – what reagents
we need to accomplish them and how they work (i.e. their reaction mechanisms). One of the key skills that
enables success is this field is an ability to search the chemical literature for different reactions: to find
precedents and test sources of information to identify reliable reactions that can be used to make a given
target molecule.
There are two sections in this assignment. You should complete both Sections 1 and 2.
Section 1 (10 marks)
This part of the assignment concerns reactions used in the synthesis of enigmazole A, a natural product isolated
from a Papua New Guinean sponge that has cytotoxic activity against cancer cell lines. Several total synthesis
routes have been reported including these two, which showcase a range of important synthetic chemistry:
Paper A: K. Sakurai, M. Sasaki, H. Fuwa, Total Synthesis of (-)-Enigmazole A, Angew. Chem. Int. Ed. 2018,
57, 5143-5146.
Paper B: C. K. Skepper, T. Quach, T. F. Molinski, Total Synthesis of Enigmazole A from Cinachyrella
enigmatica. Bidirectional Bond Constructions with an Ambident 2,4-Disubstituted Oxazole Synthon, J. Am.
Chem. Soc. 2010, 132, 10286-10292.
You have been assigned one general reaction (see last two pages of this pdf) used in one of these literature
syntheses and indicated by numbers from 1–12 in the table on page 3. For your designated reaction:
(i) (1 mark) Find an example of your assigned reaction in Paper A or Paper B. Provide a copy of the entire
Figure or Scheme (including caption) in which the reaction is shown, explicitly highlighting the step.
Note: In some cases, your designated reaction may be one step in a multi-step process.
Please do not copy the entire paper into your submission, only the relevant figure. You can download
the figure as an image file or copy as a screenshot and crop.
(ii) (6 marks) Provide a full mechanism for the general reaction, using the reagents/ reaction conditions
in the paper from part (i) and curly arrow notation as appropriate.
You may hand-draw and scan your mechanism, or use ChemDraw or another chemical drawing
program, but make sure your mechanism is clearly legible.
Provide a general mechanism only – you don’t need to draw the whole enigmazole A structure as you
show your mechanism: use R groups to abbreviate and simplify the scheme.
If your reaction occurs as part of a multistep process, just show the mechanism for your step.
(iii) Find another journal article in which the same type of reaction (i.e. that same chemical conversion:
the specific reagents used may be different) has been used in a synthesis of a different small molecule,
published in the period 2018-2023.
a. (1 mark) Provide a complete reference for this publication.
See https://en.wikipedia.org/wiki/ACS_style for an example of acceptable formatting. Please
include the publication title in your reference.
b. (2 marks) Provide a copy of the Figure or Scheme (including the caption) in which the reaction
is shown, explicitly highlighting the relevant step.
Again, don’t copy the whole paper into your submission, only the relevant figure – see above.
CHEM3118 and CHEM3918 Synthetic Chemistry – Synthesis Assignment 2023 2
Section 2 (10 marks)
This part of the assignment concerns the landmark series of alkene metathesis papers published in the
prestigious journal Nature by the Nobel Laureate Schrock and his collaborator Hoveyda:
• Paper A: M. J. Koh, T. T. Nguyen, H. Zhang, R. R. Schrock, A. H. Hoveyda, Direct synthesis of Z-alkenyl
halides through catalytic cross-metathesis, Nature, 2016, 531, 459-465 (doi:10.1038/nature17396).
• Paper B: M. J. Koh, T. T. Nguyen, J. K. Lam, S. Torker, J. Hyvl, R. R. Schrock & Amir H. Hoveyda,
Molybdenum chloride catalysts for Z-selective olefin metathesis reactions, Nature, 2017, 542, 80-86,
(doi:10.1038/nature21043).
• Paper C: T. T. Nguyen, M. J. Koh, T. J. Mann, R. R. Schrok, A. H. Hoveyda, Synthesis of E- and Z-
trisubstituted alkenes by catalytic cross-metathesis, Nature, 2017, 552, 347-356
(doi:10.1038/nature25002).
(i) (2 marks) Choose one of the three Nature papers above and indicate which one you have chosen.
Write the key general reaction scheme that summarises the reported alkene metathesis chemistry and
in one sentence summarise the key innovations of the discovery, explaining why the discovery has
transformed this type of alkene metathesis reaction.
(ii) (4 marks) Choose any one of the metal-alkylidene complexes described in the paper chosen in Section
2, part (i) (it does not need to be the most active catalyst!). Draw its chemical structure and calculate
its total valence electron count, showing all working. Please refer to Lecture 10a on electron-counting
rules for organometallic complexes.
(iii) (4 marks) Choose one synthesis of a target molecule with relevance in chemical biology or medicine
(i.e. it must be a natural product, chemical probe, or drug) using the catalytic chemistry originally
described in the Nature paper chosen in Section 2, part (i). The synthesis of the small molecule might
be reported in another paper and, if so, be sure to reference it. Draw the catalytic cycle for the alkene
metathesis reaction involving the metal-alkylidene catalyst, using the reagents/reaction conditions
described in the paper. Use curly arrow notation as appropriate. Provide only a general mechanism –
there is no need to draw the whole target molecular structure if it is too complex. Using properly
identified R-groups is acceptable. You may choose to hand-draw and scan your mechanism, or use
ChemDraw. Either way, please ensure your mechanism is clearly legible.
Resources
For searching: SciFinder
For guides and registration: http://libguides.library.usyd.edu.au/c.php?g=508175&p=3475710
For mechanistic insight: Organic Chemistry, 2nd Edition, J. Clayden, N. Greeves and S. Warren
Oxford University Press, Oxford, UK, 2012, Ebook available online via USyd Library website.
For reagents and more: e-EROS: Encyclopedia of Reagents for Organic Synthesis
Link here for online access through USyd Library
CHEM3118 and CHEM3918 Synthetic Chemistry – Synthesis Assignment 2023 3
General Reactions for Section 1
1 H R
O
S R
S
7
R' R R' R
OH OAc
2 H R
R
O
8
R
OH
R' R
OMe
R'
3 R H R
OH O
9
EtO R
O
H R
O
4
R
R'
HO
R
10
R R
HO
HO
5 R R
OH OBz
11
R
OH
R
O
HO
6 R R
OH OTBS
12
H R HO R
O O
Notes:
- Ac = acetyl
- Bz = benzoyl (different to Bn, benzyl)
- Et = ethyl
- Me = methyl
- R = any general alkyl or aryl group
- TBS = tert-butyldimethylsilyl
These syntheses and reaction steps have been chosen to take us beyond the confines of what we are able to
cover in lectures, out into the wonderful world of synthesis and beyond.
This means that many of these reactions are not ones you’ve been taught a mechanism for previously. You will
need to use your research skills, the resources listed on the previous page, and other available tools to come
up with an appropriate mechanism.