Pd-catalyzed cross-coupling of allylsilane-vinylcopper species with aryl and vinyl halides: the first total synthesis of (−)-nomadone
作者:Francisco J. Pulido、Asunción Barbero、Carlos García
DOI:10.1016/j.tet.2009.01.118
日期:2009.7
The reaction of allene with a lower order silylcuprate 3 leads to an allylsilane-vinylcopper intermediate 4, which undergoes palladium-catalyzed cross-couplingreaction with both vinyl and arylhalides. The influence of several factors such as the nature of the transition metal used as catalyst, the temperature of the reaction, and the order of addition are studied. This simple methodology allows the
Tandem Transformations Involving Allylic Silanes. 2. Highly Diastereoselective Substitutions Involving [(Trialkylsilyl)methyl]cyclohexene Derivatives with Aldehydes. Synthetic Studies on the Problem of Lewis Acid-Promoted Protodesilylation and Enolization
作者:Michael G. Organ、Derick D. Winkle、John Huffmann
DOI:10.1021/jo970821v
日期:1997.8.1
Diels-Alder cycloaddition of 2-[(trialkylsilyl)methyl]-1,3-butadienes with a variety of dienophiles and substitution reactions between these allylsilane-containing adducts and aldehyde or acid chloride electrophiles have been combined into ''tandem sequential reactions.'' These tandem sequences proceed with equal or greater yield (50-80%) than the reactions performed separately with no decrease in regio- or stereoselectivity. The sequence produces cyclic compounds with three or four stereogenic centers with good to excellent diastereoselectivity from three simple, noncyclic, and achiral reaction partners. Unprecedented levels of diastereoselectivity (de > 93%) have been achieved in allylic substitution reactions involving substituted [(trialkylsilyl)methyl]cyclohexene derivatives with aldehyde electrophiles. During the course of these studies, protodesilylation of allylsilanes has been investigated in detail, and a cocatalyst system of TiCl4 and Me2AlCl has been developed that has eliminated silicon loss in the substitution reactions studied. Lewis acid-promoted enolization of ester and ketone substrates with chiral centers adjacent to the carbonyl moiety has been studied also. It has been shown that this event in our studies occurs primarily during catalyst quench. This isomerization is prevented by quenching the catalyst with a Lewis base, such as methanol or triethylamine, prior to aqueous workup.
Allylsilane-Vinylcopper Reagents: Palladium-Mediated Coupling with Alkenyl Halides. Synthesis and Photochemical [2 + 2] Cyclization of (±)-Ipsdienol
作者:Asunción Barbero、Carlos García、Francisco J. Pulido
DOI:10.1055/s-2001-14589
日期:——
Reaction of phenyldimethylsilyl-copper with 1,2-propadiene followed by Pd0 catalyzed coupling of the resulting copper intermediate with alkenyl halides affords allylsilane-containing dienes in high yield. Coupling with vinyl bromide gives 2-phenyldimethylsilylmethylbuta-1,3-diene which is an isoprenyl building block for the synthesis of (±)-Ipsenol and (±)-Ipsdienol, the aggregation pheromones of the Ips bark beetle. The photochemical [2 + 2] cyclization of Ipsdienol was also studied.