Substrate-Controlled Domino Reaction ofN-Sulfonyl Ketimines with 2-Aroyl-1-chlorocyclopropanecarboxylates: Access to Cyclopenta[c]chromenes and Benzo[f]cyclopenta[d][1,2]thiazepine Dioxides

Abstract

An unprecedented substrate-controlled annulation method for the synthesis of fascinating classes of angularly fused cyclopenta[c]chromenes and benzo[f ]cyclopenta[d][1,2]thiazepine 5,5-dioxide derivatives in good to high chemical yields is reported. This Michael-initiated ring-expansion reaction would enable two C−C and one C−O or C−N bonds by a judicious choice of carbonucleophiles, either 4-alkyl or 3-alkyl-substituted Nsulfonyl ketimines, respectively, with a series of donor−acceptor cyclopropane scaffolds as 4C sources promoted by DBU. Moreover, this eco-friendly method is mild enough to protect different kinds of functionalities. Importantly, the prepared fused fulvene scaffolds were smoothly transformed into a special class of hexahydrocyclopenta[c]chromenes as single cis−cis−cis−cis diastereomers in excellent yields by a simple catalytic hydrogenation reaction.

Construction of heterocyclic rings from cyclopropenes

“…Using alkyl 2-benzoyl-1-chlorocyclopropanecarboxylates as the cyclopropene precursor, a class of pentafulvenefused heterocycles were synthesized through a DBU-promoted (1,8-diazabicyclo[5.4.0]undec-7-ene) reaction of N-sulfonyl ketimines at room temperature in dry 2-methylfuran. 43 The 2-pyrone motif as a key structural unit widely exists in natural products and pharmaceutically active compounds, and the bioactivity for functionalized 2-pyrones, such as 3-aryl-2pyrone derivatives, has drawn much attention as potential HIV-1 protease inhibitors. In fact, 2-pyrone can be directly constructed through the reaction of alkyl 2-aroyl-1-chlorocyclopropanecarboxylates with aliphatic amines in the presence of inorganic bases like Cs 2 CO 3 or Mg(OEt) 2 .…”

“…Using alkyl 2-benzoyl-1-chlorocyclopropanecarboxylates as the cyclopropene precursor, a class of pentafulvenefused heterocycles were synthesized through a DBU-promoted (1,8-diazabicyclo[5.4.0]undec-7-ene) reaction of N -sulfonyl ketimines at room temperature in dry 2-methylfuran. 43…”

A substrate-dependent reaction of 1-aryl-2-alkyl-1,2-diketones with 2-aroyl-1-chlorocyclopropanecarboxylates: selective access to 2′,5′-dicyclopropoxy-1,1′:4′,1′′-teraryls and pentafulvenes

“…To our delight, we also recently documented a substrate-controlled domino reaction involving 1-chloro-2-aroylcyclopropanecarboxylates and N-sulfonylketimines as carbonucleophiles triggered by DBU to build an array of fused pentafulvenes (Scheme 1c). 25 On the other hand, the research prosperity of 2-alkyl-1,2diketones has been growing in recent years due to their crucial role as reactive intermediates. 26 In contrast to electrophiles, they are scarcely used as carbonucleophilic species despite having enolizable protons.…”

“…To our delight, we also recently documented a substrate-controlled domino reaction involving 1-chloro-2-aroylcyclopropanecarboxylates and N -sulfonylketimines as carbonucleophiles triggered by DBU to build an array of fused pentafulvenes (Scheme 1c). 25…”