[5+1]-Annulation Strategy Based on Alkenoyl Ketene Dithioacetals and Analogues

Abstract

Functionalized ketene dithioacetals are versatile intermediates in organic synthesis. The important multiple roles of the dialkylthio group make these substrates particularly useful for the synthesis of a number of important classes of substituted carbo-and heterocyclic systems, such as thiophenes, lactones, pyrroles, furans, pyridines, substituted cyclohexanones, and benzene derivatives. This account focuses on the utility of alkenoyl ketene dithioacetals, which have been found useful in the synthesis of six-membered carbo-and heterocyclic systems relying upon utilization of alkenoyl ketene dithioacetals, as the 1,5-bielectrophilic component in the [5+1] annulation with carbon, nitrogen, sulfur, and other nucleophiles.

Synthesis of γ-Pyrones from Formal [4 + 2] Cyclization of Ketene Dithioacetals with Acyl Chlorides

“…In view of the importance of 2-substituted γ-pyrones and our research experience on reactions via the cleavage of the C–S bond, the transformation of the C–S bond at 2-position in γ-pyrones 3 was investigated for the synthesis of versatile γ-pyrones (Figure ). First, the arylation of γ-pyrones 3a was performed using palladium-catalyzed Liebeskind–Srogl cross-coupling reactions with arylboronic acids.…”

“…In view of the convenient utilization of widely available acyl chlorides and our continuous efforts in the development of ketene dithioacetal chemistry, − herein, we report an efficient synthesis of γ-pyrones from ketene dithioacetals 1 and acyl chlorides by an unprecedented formal [4 + 2] heterocyclization with [(CH 3 ) 3 Si] 2 NLi (LiHMDS) as the base in a single step (Scheme d). It was reported that ketene dithioacetals 1 tends to give 3-alkylthiocyclobut-2-en-1-ones via intramolecular cyclization in the presence of Bu t OK (Scheme c) or lose an acyl group in the presence of K 2 CO 3 .…”

“…Therefore, our reaction provides a novel formal [4 + 2] heterocyclization of ketene dithioacetals via the β-diketone intermediate (Scheme d) . Furthermore, combined with our previous investigations on the cleavage of the C–S bond in ketene dithioacetals, versatile transformations could be achieved affording fruitful poly-substituted γ-pyrones and fused γ-pyridones.…”

Acyl-Ethynylbenziodoxolone (acyl-EBX): Access to Ketene Dithioarylacetals

“…Ketene dithioacetals are an attractive motif in organic synthesis with a wide range of reactivity (Scheme A) . In particular, ketene dithioacetals bearing an α-carbonyl group display biological activities, such as Leishmania donovani growth inhibition .…”