Best Synthetic Methods: Carbon-Carbon Bond Construction

Abstract

In the context of peptidyl ketone synthesis, Troels Skrydstrup of the University of Aarhus developed (J. Org. Chem. 2008, 73, 1088) the elegant SmI2-mediated conjugate addition of acyl oxazolidinones such as 1 to acceptors such as 2. Sadagopan Raghavan of the Indian Institute of Chemical Technology, Hyderabad reported (Tetrahedron Lett. 2008, 49, 1601) that the addition of a Pummerer intermediate, generated by exposure of 4 to TFAA, to the terminal alkene 5 and SnCl4 led to efficient C-C bond formation, to give the sulfide 6 as a single (unassigned) diastereomer. Pd-catalyzed carbonylation of aryl halides and triflates is a well-established process. Stephen L. Buchwald of MIT has now (J. Am. Chem. Soc. 2008, 130, 2754) extended this transformation to much less expensive tosylates and mesylates such as 7. β-Amino acids have often been prepared from α-amino acids by Arndt-Eistert homologation. Geoffrey W. Coates of Cornell University has devised (Angew. Chem. Int. Ed. 2008, 47, 3979) a more practical alternative, the direct Co-catalyzed carbonylation of an oxazoline 9 to the 2-oxazine-6-one 10. Eiji Shirakawa and Tamio Hayashi of Kyoto University also used (Chem. Lett . 2008, 37, 654) a Co catalyst to promote the coupling of aryl and alkenyl Grignard reagents with enol trifl ates such as 11. Alois Fürstner of the Max-Planck-Institut, Mülheim optimized (Chem. Commun. 2008, 2873) promoters for the Pd-catalyzed Stille-Migata coupling of iodo alkenes such as 14 with alkenyl stannanes such as 15 to give 16. It is particularly noteworthy that their system is fluoride free. The stereocontrolled construction of trisubstituted alkenes continues to be challenging. We described (J. Org. Chem. 2008, 73, 1605) the facile preparation of the diioide 18 from the inexpensive 2-butyn-1,4-diol 17 . Sequential coupling of 18 with an aryl Grignard followed by CH3 Li delivered 19. Brian S. J. Blagg of the University of Kansas established (Tetrahedron Lett . 2008, 49, 141) that Still-Genari homologation of 20 with 21 gave (E)- 22 with high geometric control. Biao Jiang of the Shangahi Institute of Organic Chemistry reported (Organic Lett. 2008, 10, 593) a convenient alternative protocol to give ( Z )-α- bromo unsaturated esters.