An alkyl shift
Posted by naturalproductman on September 6, 2013
Richmond Sarpong and co-workers have reported in ACIE on a slick alkyl shift to afford (±)-3-demethoxyerythratidinone and (±)-cocculidine. I may be wrong but in Scheme 7 of the paper: going from intermediates 29 to 30 to 4, there is a loss of the enantioselectivity – the scheme shows that the final product is racemic (+/-) but the precursor 29 has 99% enantiomeric excess. Hmm.
Naturalproductman's Blog 
An Author said
I am an author on this paper. Compound 28 was enantiomerically enriched by chiral prep-HPLC and was subjected to the cycloisomerization. The %ee reported for 29 demonstrates the stereospecificity of the transformation; however, since we were preparing rac-4 in a formal synthesis and the target has been prepared many times, we elected to finish the route with racemic 29. As such, we never attempted to prepare 30 from enriched 29. Due to space constraints, we chose to use Scheme 7 to show both the formal synthesis of 4 as well as the stereospecificity of the cycloisomerization. In retrospect, this should have been more clearly explained in the text of the manuscript. We apologize for the confusion.
In any case, thanks for blogging about our work. Please let me know if you have any other questions.
naturalproductman said
Ahh I was thinking it was a formal synthesis – but it wasn’t clear from the text. Thanks for clarifying.