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...

Divergent Synthesis of Indolenine and Indoline Ring Systems by Palladium-Catalyzed Asymmetric Dearomatization of Indoles

Dearomatized indole derivatives bearing a C3- or C2-stereocenter exist ubiquitously in natural products and biologically active molecules. Despite remarkable advances in their chemical synthesis, stereoselective and regio-divergent methods are still in a high demand. Herein, a Pd-catalyzed intermolecular asymmetric spiroannulation of 2,3-disubstituted indoles with internal alkynes has been developed for the efficient construction of indoline structures with a C2-quaternary stereocenter. Stereospecific aza-semipinacol rearrangement of these indoline derivatives under acidic conditions afforded indolenine products bearing a C3-quaternary stereocenter, where the selectivity for the rearranging group could be controlled by the reaction sequence. The asymmetric spiroannulation together with the subsequent aza-semipinacol rearrangement enabled a divergent access to dearomatized indole derivatives with either a C3- or a C2-quaternary stereocenter.

Semipinacol rearrangement of a bicyclo[7.2.0]undecane framework into a bicyclo[6.3.0]undecane skeleton: A model study on the biosynthesis of seiridiasteriscane A

Seiridiasteriscane A is an asteriscane-type sesquiterpenoid bearing a trans-fused bicyclo[6.3.0]undecane skeleton. Although its biosynthesis has been proposed to involve a semipinacol rearrangement of a putative intermediary acetate bearing a bicyclo[7.2.0]undecane ring system (presumably derived from co-isolated pestalotiopsin M) followed by epimerization of the resulting cis-fused seiridiasteriscane B, such a type of semipinacol rearrangement has never been reported so far. Our model study revealed that a 1-hydroxybicyclo[7.2.0]undecan-2-yl acetate underwent a smooth and stereospecific semipinacol rearrangement with the assistance of Et2AlCl to give the corresponding bicyclo[6.3.0]undecane-9-one. In addition, the resulting cis-fused 5,8-bicyclic ketone was partially epimerized to the corresponding trans-fused ketone by prolonged adsorption onto a silica gel plate. These results may support a recently proposed biosynthetic pathway of seiridiasteriscane A.

Recent development and applications of semipinacol rearrangement reactions

The recent development of semipinacol rearrangement is reviewed, highlighting its application in β-functionalized ketone synthesis, quaternary carbon formation and total synthesis.

Construction of the Tetracyclic Core of the Lycopodium Alkaloid Annotinolide C

A concise method of synthesizing the tetracyclic core of annotinolide C has been developed. The key steps feature a tandem epoxidation/semipinacol rearrangement step to construct an aza quaternary aza [6.5]...

Oxyallyl Cation Promoted Dearomative Semipinacol Rearrangement: Facile Stereodivergent Synthesis of Spiro-indolines with Contiguous Quaternary Centers

A novel oxyallyl cation promoted semipinacol rearrangement of indole-type allylic alcohols was disclosed for the stereo-divergent synthesis of spiro-indolines. A variety of spiro-indolines were obtained with moderate to good yields....

Photoredox-mediated N-centered Radical Addition/Semipinacol Rearrangement for the Convenient Synthesis of β-Amino (spiro)Cyclic Ketones

A visible light photoredox-catalyzed N-centered radical addition/semipinacol rearrangement cascade of cycloalkanol-substituted 1H-indenes or styrenes with arylsulfonyl protected 1-aminopyridinium salts is presented. This protocol offers an efficient access to β-amino (spiro)cyclic...