Facile Enantioselective Synthesis of Propargylic Alcohols by Direct Addition of Terminal Alkynes to Aldehydes

Enantioselective Synthesis of (+)-Cephalostatin 1

“…The Swern reagent chemoselectively converted the TMS ether of the primary carbinol directly into aldehyde 38. Carreira alkynylation 19 , resulted in quantitative spiroketalization; 24 however, the undesired C22-(R) spiroketal stereoisomer was favored by a 13:1 ratio. This may be due to HCl generated during the reaction and attempts to buffer the reaction with nitrogenous bases inhibited spiroketalization.…”

Total synthesis of antibiotics: recent achievements, limitations, and perspectives

“…The second fragment was quickly made by N-methylephedrinecatalyzed asymmetric addition of propyne to a TBS-protected -hydroxypropanal according to the Carreira protocol. (Frantz, 2000) The third precursor was also easily obtained using asymmetric crotylsilylation methodology developed by the same group. The reductive alkyne-alkyne coupling (Reichard, 2008) In the present case, the coupling of 30 and 31 under conditions described above provided diene 37 in 58% yield (Scheme 5).…”

Enantioselective Total Synthesis of (−)‐Acylfulvene and (−)‐Irofulven

“…An approach based on asymmetric alkynylation of aldehyde 37 followed by substrate directed epoxidation also did not provide the desired C2-stereocenter. 19 While Carreira's alkynylation reaction provided the desired product 38 with excellent stereoselectivity (99% ee) using superstoichiometric Zn(OTf) 2 and N-methylephedrine (NME), the subsequent epoxidation of the allylic alcohol 38 using metachloroperbenzoic acid (mCPBA) resulted in the formation of a complex mixture of products. Since oxidation reactions 20 aimed at forming the stereocenter adjacent to the cyclopropane proved to be problematic, we pursued an alternative route.…”