Efficient synthesis of ethyl 2-(oxazolin-2-yl)alkanoates via ethoxycarbonylketene-induced electrophilic ring expansion of aziridines

Alkyl 2-diazo-3-oxoalkanoates generate alkoxycarbonylketenes, which undergo an electrophilic ring expansion with aziridines to afford alkyl 2-(oxazolin-2-yl)alkanoates in good to excellent yields under microwave heating. The method is a convenient and clean reaction without any activators and catalysts and can be also applied in the synthesis of 2-(oxazolin-2-yl)alkanamides and 1-(oxazolin-2-yl)alkylphosphonates.

Acid-Catalyzed Ring-expansion of 4-(1-hydroxycyclobutyl)-1,2,3-triazoles

We here reported a direct ring-opening/semipinacol rearrangement reaction of 4-(1-hydroxycyclobutyl)-1,2,3-triazole, in which N-acyl substituted 1,2,3-triazole was generated in situ and would trigger thermodynamically controlled electrocyclization ring-opening to afford rearrangement precursor...

Stereoelectronic and Dynamical Effects Dictate Nitrogen Inversion during Valence Isomerism in Benzene Imine

Benzene imine (1) ⇌ 1H-azepine (2) isomerization occurs through sequential valence and endo–exo isomerism. Quantum chemical and quasiclassical trajectory (QCT) simulations reveal the coupled reaction pathway ‒ ring-expansion followed by...

Aza-Yang Cyclization—Buchner Aromatic Ring Expansion: Collective Synthesis of Cycloheptatriene-containing Azetidine Lactones

We prepared a collection of complex cycloheptatriene-containing azetidine lactones by ap- plying two key photochemical reactions: “aza-Yang” cyclization and Buchner carbene insertion into aromatic rings. While photolysis of phenacyl amines leads to a rapid charge transfer and elimination, we found that a simple protonation of the amine enables the formation of azetidinols as single diastereomers. We provide evidence, through ultrafast spectroscopy, for the electron transfer from free amines in the excited state. Further, we characterize aza-Yang re- action by establishing the dependence of initial reaction rates on rates of photon absorption. Unanticipated change in reactivity in morpholine analogs is explained through interactions with the tosylate anion. Buchner reaction proceeds with slight preference for one diastereomer over the other, and successful reaction requires electron-donating carbene-stabilizing substituents. Overall, sixteen compounds were prepared over seven steps. Guided by an increase in structural complexity, efforts such as this one extend reach of chemists into unexplored chemical space and provide useful quantities of new compounds for studies focused on their properties.