Tag Archives: Wolff rearrangement

Carbynes ! ! !

An article on carbynes brought back memories of the Spring of 1961 when I convinced Woodward to let me work on an original idea about carbenes for my PhD thesis.  Back then you had to pass 8 cumulative exams (given monthly) before you could start such work.  It took me 9.

At the time, carbenes were a rather speculative idea, but it seemed to me that they could be generated by photolysis of a diazocarbonyl compound. I thought they might be involved in the Wolff rearrangement

One of the joys of organic chemistry back then (and hopefully now) is that if you have an idea, just build a molecule to test it.

So here’s the idea the great man bought.

l. Condense acrylic acid with cytopentadiene by a Diels Alder reaction.  Because of steric effects the acid will point below the ring system

2. Form the acyl chloride

3. React with diazoMethane to form the diazocarbonyl — there will be no change in the orientation of the carbonyl relative to the ring system

4. Photolyze — a a carbene is formed it would be in perfect position to form a cyclopropane on the other side of the ring system, pretty much proving its existence.

Malheureusement, having the worst lab technique in the world and being very frightened by what I’d heard about diazoMethane, I couldn’t get the idea to work.

However the idea was good, and a friend who kept on in chemistry becoming a department head told me that I was right.

Which brings us to the current article [ Nature vol. 554 pp. 36 – 38, 86 – 91 ’18 ] http://www.nature.com/magazine-assets/d41586-018-01308-7/d41586-018-01308-7.pdf.

A carbyne is basically R – C where the carbon has 3 electrons not forming covalent bonds (two are paired).  As you might imagine, carbynes are quite reactive.  However both articles talk about a carbyne equivalent which is R – C = N2, which IMHO is not a carbyne at all.  It is intrguing that it would be if the N2 were photolyzed off a la 1961, but that isn’t what happens in the paper.  It remains as the intermediate performs all sorts of interesting chemistry, forming an Aryl – C (R) = N2 moiety etc. etc.

One interesting aside is that carbynes were one of the first molecules found in interstellar space.

Can anyone out there enlighten me as to why R – C = N2 is a carbyne equivalent.  Neither paper provides an explanation.