Nitrogen insertion reactions of bridged bicyclic ketones. Regioselective lactam formation

2-Azabicyclo[3.2.1]octane scaffold: synthesis and applications

2-Azabicyclo[3.2.1]octanes are nitrogen containing heterocycles with significant potential in the field of drug discovery. This core has been applied as key synthetic intermediate in several total synthesis, while their unique structure can make them a challenging scaffold to acquire. This Minireview summarizes the synthetic approaches to access this bicyclic architecture and highlights its presence in the total synthesis of several target molecules.

Substituent effects on intramolecular Schmidt reactions: a theoretical study on the formation of bridged lactams

The competitive formation of isomeric bridged lactams via acid-catalyzed intramolecular Schmidt reactions from 3-azidoethylcyclopentanones is explored using density functional theory (DFT) calculations, primarily performed at the M06-2X/6-311++G(d,p) level of theory. The results indicate that specific substituents installed at α-carbons can efficiently control the regioselectivity of the reaction by lone pair-cation interactions or steric hindrance reversing the main product preference, whereas cation-π interactions are not so effective.

Metal-free synthesis of secondary amides using N-Boc-O-tosylhydroxylamine as nitrogen source via Beckmann rearrangement

An efficient methodology for the direct synthesis of secondary amides from ketones has been developed by using N-Boc-O-tosylhydroxylamine (TsONHBoc).

Toward the Scale-Up of a Bicyclic Homopiperazine via Schmidt Rearrangement and Photochemical Oxaziridine Rearrangement in Continuous-Flow

The scale-up of a chiral bicyclic homopiperazine of pharmaceutical interest was investigated. The outcome and safety profile of a key batch ring-expansion step via Schmidt rearrangement was improved using continuous-flow chemistry. The selectivity of nitrogen insertion for the ring expansion was improved via an alternative photochemical oxaziridine rearrangement under mild conditions, which when converted to continuous-flow in a simple and efficient flow reactor allowed the first photochemical scale-up of a homopiperazine.

Silica Sulfuric Acid as a Reusable Catalyst for the Conversion of Ketones into Amides by a Schmidt Reaction under Solvent-Free Conditions

Silica sulfuric acid is a highly efficient reagent for the conversion of a variety of ketones into the corresponding amides by a Schmidt reaction under solvent-free conditions. Cyclic, aliphatic and aromatic ketones with electron-donating or withdrawing substituents may be converted easily in excellent yield. The major advantages of this method are: operational simplicity, the ready availability of the reagent, selectivity, general applicability, mild reaction conditions, short reaction times and high yields. The recovered catalyst could be used in new attempts without any purification.

Simple synthesis of conformationally fixed glycosamine analogues by beckmann rearrangement at the carbohydrate ring

Conformationally fixed carbohydrate analogues are promising small-molecule inhibitors for hydrolases like O-GlcNAcase (OGA); however, their synthesis usually requires many steps. Herein we describe cycloadditions of dichloroketene to various glycals and subsequent Beckmann rearrangements, which offer an easy and stereoselective entry to glycosamine derivatives in good yields. The reactions are applicable for hexoses, pentoses, and disaccharides, and transformations to the corresponding imidates proceed smoothly. First biological tests reveal that such imidates indeed inhibit human OGA.

Concise access to indolizidine and pyrroloazepine skeleta via intramolecular Schmidt reactions of azido 1,3-diketones

Readily prepared 2-alkyl-2-azidopropylcycloalkyl-1,3-diones undergo intramolecular Schmidt rearrangement with a range of hard Lewis acids, leading to indolizidinediones and pyrroloazepinediones. Chiral aluminium-based Lewis acids could also be used to mediate this symmetry-breaking transformation, but no significant asymmetric induction was observed.