Preparation and reactivity of highly functionalized organometallics at the .alpha. position of oxygen or nitrogen
摘要:
Alpha-Halogenoalkyl carboxylates (FG-R1CH(X)(OCOR2); FG = COOR, CN, SR; X = I, Br) were readily prepared by the addition of an acid chloride or bromide (R2COX; X = Br or Cl) to an aldehyde (FG-RCHO) in the presence of a catalytic amount of ZnCl2. They insert efficiently zinc dust in THF-DMSO (X = Br, 8-10-degrees-C, 6-10 h) affording the corresponding zinc organometallics at the a position to oxygen FG-RCH(ZnBr)(OAc). After the addition of the THF-soluble copper salt CuCN.2LiCl, the corresponding copper reagents FG-RCH(Cu(CN)ZnBr)(OAc) are formed and reacted with various classes of electrophiles such as acid chlorides, aldehydes, enones, allylic and alkynyl halides, activated alkynes, nitro olefins and alkylidenemalonates providing polyfunctional molecules in excellent yields. Similarly, zinc organometallics at the a position to the nitrogen of cyclic imides were prepared by the zinc insertion to cyclic alpha-chloromethyl (or alpha-chloroethyl) imides. After their transmetalation to the corresponding copper organometallic ((R1CO)2NCH(R)(Cu(CN)ZnCl); R = Me or H), they were reacted with allylic and alkynyl halides and ethyl propiolate affording polyfunctional imides. The reaction of cyclic N-(chloromethyl)imides with aldehydes in the presence of chromium(II) chloride in THF furnishes protected amino alcohols in 36-95% yield.
Combined Effects on Selectivity in Fe-Catalyzed Methylene Oxidation
作者:Mark S. Chen、M. Christina White
DOI:10.1126/science.1183602
日期:2010.1.29
in organic molecules. Methylene C–H bonds are among the most difficult chemical bonds to selectively functionalize because of their abundance in organicstructures and inertness to most chemical reagents. Their selective oxidations in biosynthetic pathways underscore the power of such reactions for streamlining the synthesis of molecules with complex oxygenation patterns. We report that an iron catalyst