DBU‐Catalyzed Ring‐Opening and Retro‐Claisen Fragmentation of Dihydropyranones

Abstract

We present a general protocol for the formal Michael addition of acetone to α,β‐unsaturated esters and amides, a transformation difficult to perform using current methods. The protocol comprises of an amidine catalyzed relay ring‐opening and fragmentation of 3,4‐dihydropyranones. The reaction proceeds under mild conditions, has a broad substrate scope and the products can be isolated in good to excellent yields. The method can be applied to homochiral substrates with total preservation of chiral information, generating products in high optical purity. Kinetic experiments supported by quantum chemical modeling indicate a mechanism in which the catalyst takes a bifunctional role, acting both as a Brønsted base and as a hydrogen‐bond donor.

Diamine‐Promoted Deacylation of 2‐Alkyl‐1,3‐Diketones for the Facile Synthesis of Ketones

“…This was confirmed using γ ‐aminopropanol ( 2 l ), primary amine 2 m , [23] secondary amine 2 n , cyclic amine 2 o , [36] and tertiary amine 2 p , whose reactions proceeded significantly more slowly to give mainly the starting diketone 1 a (Table 1, entries 12–16). However, DBU was found to efficiently promote the retro‐Claisen reaction (Table 1, entry 17) [21b,c,37] . This is an interesting result as DBU failed to promote the present deacylation in toluene, a nonpolar solvent, thereby indicating that 1,3‐diketone, which decomposes into a protic solvent, could be used.…”

Recent Advances in the Synthesis of 3,4-Dihydropyran-2-Ones Organocatalyzed by N-Heterocyclic Carbenes

“…It should be noted that products 3 and 4 have been derivatized and s actions such as epoxidations [39], alkylations [40], and ring-openings [41] It should be noted that products 3 and 4 have been derivatized and subjected to reactions such as epoxidations [39], alkylations [40], and ring-openings [41] that preserve chirality.…”

Improving the steric hindrance effect of linear sulfonated acetone–formaldehyde dispersant and its performance in coal–water slurry

“…42 In the second stage, formaldehyde and acetone begin to polymerize based on aldol condensation and a Michael addition reaction mechanism (iii). 43,44 In the nal stage, the addition product of phenol and sodium bisulte reacts with the a-C in a prepolymer of formaldehyde and acetone 42 to generate a new C-C bond. At the same time, this prepolymer will further polymerize with formaldehyde and acetone to form the nal dispersant.…”