52053-12-0Relevant articles and documents
Synthesis and reactivity of chiral alkoxyallenes prepared by carbocupration of propargylic acetals.
Marek, I.,Alexakis, A.,Mangeney, P.,Normant, J. F.
, p. 171 - 190 (2007/10/02)
Chiral propargylic acetals are easily prepared with a chiral diol having a C2 axis of symmetry.They react highly diastereoselectively with Grignard reagents, under CuI catalysis, to afford axially chiral alkoxy allenes.The process is believed to involve a syn addition of the organometallic reagent across the triple bond, followed by a selective anti β-elimination of the alkoxy moiety next to the pseudoaxial substituent of the acetal ring.Although these chiral alkoxy allenes slowly racemize in the presence of CuI salts it is possible to slow down this processby addition of trivalent phosphorus ligands.In the absence of any copper salt, such preformed alkenyl organometallic reagents (Li, Mg) also undergo a highly diastereoselective β-elimination (de > 90percent).These chiral alkoxy allenes react further with lithium dialkyl cuprate to afford the E or Z enol ether (according to the reaction condition) leading, after hydrolysis, to chiral β-disubstituted aldehydes. Key Words: chiral diols / propargylic acetals / alkoxy allenes / organocuprates / enol ether E and Z / β-disubstituted aldehydes
