For people who say that inflation of yields is a new thing... think again. Corey's synthesis of gibberellic acid is otherwise really quite good.
Note: I'm currently on holiday. I do have internet access, but drawing chemical structures on the netbook I've borrowed may just be too painful. I'll try and get some updates out ASAP.
Di-t-butylisobutylsilyl, Another Useful Protecting Group
I suspect that anybody who’s been engaged in synthetic chemistry for more than a year or two has probably used a silicon protecting group. I’ve used plenty, and they’re generally very useful, easy to put on and take off, and pretty robust under a lot of different conditions. One of the great things about these groups is the huge range available; from the labile TMS and TES, to the more robust (and useful) TBS and TBDPS, to the hardy TIPS. At the extreme end of the scale an even tougher group is the tri-t-butylsilyl group, but that’s very hard to put on or take off, and the silylating reagent itself is a pain to make. This week Corey published an attempt to fill the niche for a group tougher than TIPS, but more useful than tri-t-butylsilyl, with the disclosure of the di-t-butylisobutylsilyl (BIBS) group.
Dear internet, I'm a little busy this weekend, so please accept this rambling semi-rant and I promise I'll put up some real content soon.
Has anyone else noticed the variety of arrows used in retrosyntheses in the literature? A lot of people seem to be using closed arrows these days (for a recent example from someone who should know better, see the abstract of Baran's cortistatin full paper from last month), rather than the more traditional open ended ones (Þ). I can't easily give an example of the incorrect kind above, because as far as I can tell there isn't a character for it in any font. That's because, as far as I know, it doesn't mean anything. The open arrow, on the other hand, predates the concept of retrosynthesis by a long way, as it's the logical operator for the implication relation. So A Þ B means that the presence of A implies B. Which kind of makes sense. Eager to find a supportive quote from E. J. Corey, who coined the term retrosynthesis, I dug out my copy of The Logic of Chemical Synthesis, and was pleased to find the following:
"It is customary to use a double arrow (Þ) for the retrosynthetic direction in drawing transforms..."
Excellent. However, during my search this sentence in the preceding paragraph caught my eye:
"Woodward’s account of the state of “organic” synthesis in a volume dedicated to Robert Robinson on the occasion of his 70th birthday indicates the spirit of the times. Long multistep syntheses of 20 or more steps could be undertaken with confidence despite the Damocles sword of synthesis - only one step need fail for the entire project to meet sudden death."
I've never heard anyone talk about the "Damocles sword of synthesis" before, but I think it nicely describes the feeling of impending doom which I've felt a few times during my time as a synthetic chemist. If you didn't get the benefit of a classical education, let me explain the origin of this phrase (with a little help from the wikipedia article).