Diastereoselective Synthesis of Biheterocyclic Tetrahydrothiophene Derivatives via Base-Catalyzed Cascade Michael-Aldol [3 + 2] Annulation of 1,4-Dithiane-2,5-diol with Maleimides

Abstract

A highly diastereoselective intermolecular [3 + 2] annulation of 1,4-dithiane-2,5-diol to maleimides has been developed by using DABCO as a catalyst, which provides a series of highly functionalized biheterocyclic tetrahydrothiophene derivatives containing tetrahydrothiophene and pyrolidine backbones in excellent yields and diastereoselectivities (up to 98% yield and >20:1 d.r.). The cascade Michael-aldol reaction is capable of tolerating organic solvents as well as water.

Properties of a Newly Identified Acetyl Esterase and Its Degradation of Diisobutyl Phthalate

“…Esterases specifically act on ester bonds, forming corresponding monoesters and alcohols or phthalic acid. [11] As reported recently, the existing hydrolases can degrade PAEs, such as the esterolytic thermostable esterase EstS1 of Bacillus acidophilus DSM10332, [12] and the ester hydrolase PatE of Rhodococcus rhodococcus RHA1. [13] However, there are few studies on using esterases to degrade the PAE -diisobutyl phthalate (DiBP).…”

3‐Arylidene‐4‐Chromanones and 3‐Arylidene‐4‐Thiochromanones: Versatile Synthons towards the Synthesis of Complex Heterocycles

“…The reaction proceeds via an apparent intermolecular [3+2] annulation strategy. The mercaptoacetaldehyde generated from 1,4‐dithiane‐2,5‐diol 120 under equilibrium conditions could be activated by the tertiary bicyclic amine moiety of the catalyst 121 to form an intermediate which undergoes sulfa Michael addition followed by intramolecular aldol reaction through nucleophilic attack of the in‐situ enolate of the chromanone moiety to the aldehyde moiety of the mercaptoacetaldehyde intermediate leading to the spiro[chromane‐3,3′‐thiophen]‐4‐ones 122 in a diastereoselective fashion [126] . The enantioselectivity is brought out by the chiral squaramide catalyst 121 which hinders one face of the enolate moiety leading to one particular enantiomer depending on the type of the chiral catalyst (Scheme 42).…”

Catalyst‐free 1,6‐Conjugate Addition of S‐Nucleophiles to para‐Quinone Methides

“…[3] Among them, commercially available 1, 4-dithiane-2, 5-diol containing multiple reactive sites has been employed as a versatile synthetic precursor in the construction of sulfur-containing compounds (Scheme 1). [4] This type of precursor usually serve as a three-atom unit in [3 + n] cycloadditions, and undergo a cascade sulfa-Michael/aldol condensation process with a wide range of olefins, [5] imines, [6] 1,3-dipoles, [7] and other substrates, [8] respectively. Meanwhile, it can also act as a 1,2-bisnucleophile partner in formal [2 + 3] cycloadditions with allenoate, [9] α,β-unsaturated aldehyde, [10] 1,3-enyne, [11] or activated donor-acceptor cyclopropanes, [12] which provide a facile and straightforward access to fully substituted or polycyclic thiophenes.…”