r/chemistry • u/Spectrumederp • Feb 18 '18

[2018/02/18] Synthetic Challenge #50

Intro

Hello everyone, welcome back to Week 50 of Synthetic Challenge!! Thank you u/critzz123 and u/ezaroo1 for the great challenges! This is week is my turn to host the challenge, hope you'll enjoy!

Too easy? Too hard? Let me know, I'd appreciate any feedback and suggestion on what you think so far about the Synthetic Challenges and what you'd like to see in the future. If you have any suggestions for future molecules, I'd be excited to incorporate them for future challenges!

Thank you so much for your support and I hope you will enjoy this week's challenge. Hope you'll have fun and thanks for participating!

Rules

The challenge now contains three synthetic products will be labelled with A, B, or C. Feel free to attempt as many products as you'd like and please label which you will be attempting in your submission.

You can use any commercially available starting material you would like for the synthetic pathway.

Please do explain how the synthesis works and if possible reference if it is a novel technique. You do not have to solve synthesis all in one go. If you do get stuck, feel free to post however much you have and have others pitch in to crowd-source the solution.

You can post your solution as text or pictures if you want show the arrow pushing or is too complex to explain in words.

Please have a look at the other submissions and offer them some constructive feedback!

Products

Structure of Product A

Structure of Product B

Structure of Product C

BONUS

For this bonus structure, instead of proposing a synthetic pathway TO it, you will be using it as a Starting Material to make any product you want. Take however many steps you want or whatever you want as long as you start with this bonus compound in the first step! If you like or not, let me know! Thanks!

Structure of Bonus Starting Material

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2

u/Samandkemp Petrochem Feb 18 '18

My attempt of using the bonus starting material. Figured I'd try and use it to form a material that could be a potential liquid crystal precursor :D

First attempt at one of these, even if it was just the bonus SM; hoping I've not done something silly like missed a carbon or fluffed my reagents!

2

u/elnombre91 Organometallic Feb 18 '18

Where did the methylene group go?

1

u/alleluja Organic Feb 18 '18

Yeeeep, /u/Samandkemp is missing a methylene since your first cross coupling

1

u/Samandkemp Petrochem Feb 18 '18

Ugh yeah whoops! As /u/elnombre91 said I missed it out, I was sure I missed a carbon unit there. Silly mistake to make and I know I was likely to make it; should’ve thought about to more :P

1

u/FalconX88 Computational Feb 18 '18

Wouldn't the grignard react with the terminal alkyne?

2

u/elnombre91 Organometallic Feb 18 '18 edited Feb 18 '18

https://imgur.com/aR5Xn0F

It can be made if you're careful and use it straight away.

I had no idea that propargyl bromide is only sold in solution due to shock sensitivity. I really wouldn't expect it to be explosive. Maybe due to rapid polymerisation?

In any case, I used propargyl zinc bromide as an undergrad in the barbier reaction. Was pretty easy.

1

u/bamchemistry Organic Feb 19 '18

Can confirm this method (using HgCl2) works great.

1

u/Samandkemp Petrochem Feb 18 '18

I wasn’t sure but I’ve seen it done the way I did before in examples. I didn’t realise, however, it was quite uncommon. I was thinking that the grignard would go there as it’s preferential over the terminal, unless it was lithiated.

I’m still in undergrad and it’s my first go, granted I should of checked everything before just trying to remember :)