18815-74-2Relevant articles and documents
Rhodium-Catalyzed Desymmetrization of meso -Glutaric Anhydrides to Access Enantioenriched anti, anti -Polypropionates
Cochran, Brian M.,Henderson, Daniel D.,Thullen, Scott M.,Rovis, Tomislav
, p. 306 - 309 (2018)
An expedient desymmetrization of 3,5-dimethyl-4-alkoxyglutaric anhydrides to access anti, anti -polypropionates is described. The previously unknown anhydrides are rapidly assembled from readily available precursors. A Rh(I)· t -BuPHOX catalyst system was found to provide good yield and high selectivities. With these conditions, the trisubstituted anhydrides were desymmetrized with various alkyl zinc reagents to provide synthetically useful enantioenriched anti,anti -2,4-dimethyl-3-hydroxy-δ-ketoacids. An identical catalyst system also affords access to syn, syn -stereotriads as well as a partial kinetic resolution of a chiral anhydride.
The Catalytic Alkylative Desymmetrization of Anhydrides in a Formal Synthesis of Ionomycin
Oberg, Kevin M.,Cochran, Brian M.,Cook, Matthew J.,Rovis, Tomislav
supporting information, p. 4343 - 4350 (2018/06/08)
The catalytic desymmetrization of anhydrides with zinc reagents provides access to deoxypolypropionate and polypropionate synthons. A synthesis of ionomycin was pursued in which three of the four fragments were assembled using this methodology. Two of the strategies (enol silane/oxocarbenium coupling and reductive cyclization) were not successful at installing the C23 stereocenter, but this stereochemical issue was overcome through a reduction/S N 2 approach. In addition to the synthesis of a protected diastereomer of ionomycin, the synthesis of a C17-C32 fragment constitutes a formal total synthesis.
Overriding felkin control: A general method for highly diastereoselective chelation-controlled additions to α-silyloxy aldehydes
Stanton, Gretchen R.,Johnson, Corinne N.,Walsh, Patrick J.
, p. 4399 - 4408 (2010/06/14)
According to the Felkin-Anh and Cram-chelation models, nucleophilic additions to α-silyloxy aldehydes proceed through a nonchelation pathway due to the steric and electronic properties of the silyl group, giving rise to Felkin addition products. Herein we describe a general method to promote chelationcontrol in additions to α-silyloxy aldehydes. Dialkylzincs, functionalized dialkylzincs, and (E)-disubstituted, (E)-trisubstituted, and (Z)-disubstituted vinylzinc reagents add to silyl-protected α-hydroxy aldehydes with high selectivity for chelation-controlled products (dr of 10:1 to 20:1) in the presence of alkylzinc halides or triflates, RZnX. With the high functional group tolerance of organozinc reagents, the mild Lewis acidity of RZnX, and the excellent diastereoselectivities favoring the chelation-controlled products, this method will be useful in the synthesis of natural products. A mechanism involving chelation is supported by (1) NMR studies of a model substrate, (2) a dramatic increase in reaction rate in the presence of an alkylzinc halide, and (3) higher diastereoselectivity with larger alkyl substituents on the α-carbon of the aldehyde. This method provides access to chelation-controlled addition products with high diastereoselectivity previously unavailable using achiral organometallic reagents.
