Application of stereocontrolled aldol coupling to synthesis of segments of immunosuppressants FK-506 and rapamycin
作者:James D. White、Jörg Deerberg、Steven G. Toske、Takayuki Yakura
DOI:10.1016/j.tet.2009.06.030
日期:2009.8
The sector comprising C24–C34 of FK-506 containing five of the stereogenic centers in this macrolide was synthesized from (−)-quinic acid. Aldol coupling of the C24–C34 unit with a methyl ketone representing C20–C23 of FK-506 proceeded with complete Felkin stereoselectivity to afford the C20–C34 portion of the immunosuppressant. A chelate transition state invoking coordination of a lithium enolate
An efficient method for targeting a variety of symmetrical and asymmetrical α-substituted dithiomalonates (DTMs) is described, utilizing 1H-imidazole-1-carbothioates as reactive acylating agents and MgBr2⋅OEt2/DBU or LiHMDS for soft or hard enolization conditions of thioesters, respectively. The utility of this methodology was demonstrated through the synthesis of the pyridopyrimidine mesoionic insecticides: