Three-Component Glycolate Michael Reactions of Enolates, Silyl Glyoxylates, and α,β-Enones

Abstract

Silyl glyoxylates react with enolates and enones to afford either glycolate aldol or Michael adducts. Product identity is controlled by the countercation associated with the enolate. Reformatsky nucleophiles in the presence of additional Zn(OTf)2 result in aldol coupling (A), while lithium enolates provide the Michael coupling (B). Deprotonation of the aldol product A with LDA induces equilibration to form the minor diastereomer of Michael product B. This observation suggests that formation of the major diastereomer of Michael product B does not occur via an aldol/retro-aldol/Michael sequence.

Iminoiodane- and Brønsted Base-Mediated Cross Dehydrogenative Coupling of Cyclic Ethers with 1,3-Dicarbonyl Compounds

“…1). This test gave 4n along with a 1:1 mixture of 2a and 3n in 35% and 43% yield, respectively, with the latter two adducts being obtained, presumably, from a competitive retro-Mannich-type pathway [113,114,115,116,117,118]. The role of DBU in mediating the cyclization of the 1,4 amino aldol was also supported by our findings showing the recovery of the substrate on treating it to the standard conditions in the absence of the Schiff base (Scheme 3, Equation (2)).…”

Stereocontrolled Formation of Several Carbon–Carbon Bonds in Acyclic Systems

“…The regioselectivity of the addition on the Michael acceptor is dependent on the nature of the nucleophilic enolate. For instance, lithium enolate 18 in the presence of LiCl leads to the 1,4-addition product 19 , whereas addition of zinc salt to 18 gives preferentially the 1,2-addition product 20 (Scheme , path C) …”

“…For instance, lithium enolate 18 in the presence of LiCl leads to the 1,4-addition product 19, whereas addition of zinc salt to 18 gives preferentially the 1,2-addition product 20 (Scheme 7, path C). 17 This methodology was applied to the preparation of Trachyspic acid from undecanal. 18 The key step is the threecomponent silyl glyoxylate coupling that afforded up to 4.9 g of the desired ketone 21 possessing the two critical stereogenic centers through the formation of two carbon−carbon bonds (Scheme 8).…”

Brønsted Acid Catalyzed Highly Diastereoselective Michael‐Type Addition of Azlactones to Enones

“…In our research program, we envisioned that Brønsted acid catalysis could be an attractive, metal‐free strategy to perform the reaction between azlactones and enones. Moreover, it would be very interesting if this method could be extended to the diastereoselective desymmetrization of dibenzylidene acetone (dba), which has not yet been reported 9. In this communication, we report the results of the Brønsted acid catalyzed stereoselective addition of azlactones to enones.…”