0 Hits

  • Previous / Next

You are using Science Of Synthesis as a Guest.
Please login to access the full content or check if you have access via Variation 1: Titanium-Catalyzed Cycloaddition

DOI: 10.1055/sos-SD-046-00090

Gandon, V.; Thorimbert, S.; Malacria, M.Science of Synthesis, (200946186.

A problem inherent in the syntheses of cyclohexa-1,3-dienes from simple alkynes is competitive [2+2+2] cyclotrimerizations that give benzenes.[‌53‌,‌55‌,‌57‌,‌58‌,‌61‌‌65‌] A solution to this problem is found in the use of a titanacyclopentadiene [obtained by the sodium amalgam reduction of a bis(aryloxy)dichlorotitanium in the presence of an alkyne] to catalyze the chemo- and stereoselective cocyclizations of unelaborated alkynes such as hex-3-yne, 3,3-dimethylbut-1-yne, and (trimethylsilyl)acetylene with simple alkenes including ethene, trimethyl(vinyl)silane, and styrene. For instance, metallacycle 48 can be prepared from complex 47 and hex-3-yne, and this catalyst may then promote the stereoselective cocy­clization between hex-3-yne and ethene to give (5R*,6R*)-1,2,5,6-tetraethylcyclohexa-1,3-diene (49) (Scheme 19); note that the diene framework of this product is shifted compared to that of the expected isomer.[‌66‌] Despite the fact that this method favors alkyne/alkene cocyclization over alkyne cyclotrimerization, mixtures of regioisomers are often formed.

Meeeee 88 M Meeeeeee-Meeeeeeee Meeeeeeeeeeee eeeeeee Mee-8-eee eee Meeeee[‌88‌]