Derailed Ohira‐Bestmann Reaction of γ , δ ‐Unsaturated Aldehydes for the Stereoselective Synthesis of Cyclopenta[ c ]pyrazoles

Recent approaches towards one-carbon homologation-functionalization of aldehydes

One-carbon homologation-functionalization in organic synthesis is a quite challenging and difficult task in terms of atom economy, ease of reaction, selectivity and number of steps involved. Due to the reactivity associated with most classes of carbonyls, these groups have always attracted a great deal of attention from synthetic chemists to transform them into various functionalities. In this context various researchers developed new methods for one-carbon extension-functionalization of carbonyls that serve as effective synthetic methodologies and are widely used in target-oriented and natural product synthesis. On account of the vast applicability associated with these transformations, herein we seek to summarize and highlight the important synthetic achievements in this advancing arena for various one-carbon homologation cum functionalization reactions of aldehydes and deep dive into some modern approaches adopted by organic chemists.

TFA-mediated synthesis of functionalized pyrano[2,3-c]pyrazoles from pyrazol-3-ones, active carbonyl compounds and tert-BuOH

Functionalized pyrano[2,3-c]pyrazoles were synthesized from 2,4-dihydro-3H-pyrazol-3-ones, active carbonyl compounds and tert-BuOH in the presence of trifluoroacetic acid at 65 °C. These reactions are proceeded by acid catalyzed generation of isobutylene from tert-BuOH for LUMO_diene-controlled inverse [4 + 2] cycloaddition reaction with in situ-generated vinylidenepyrazolones.

An overview of the reactions involving azomethine imines over half a decade

Azomethine imines constitute a versatile class of 1,3-dipoles which was used extensively for biologically relevant N-heterocycle synthesis – a five-year recap.

The Bestmann-Ohira Reagent and Related Diazo Compounds for the Synthesis of Azaheterocycles

Azaheterocycles are one of the most prevalent classes of compounds present in numerous bioactive compounds, natural products, and agrochemicals, and undoubtedly, new methods to access them are always in high demand. Among the methods available, the 1,3-dipolar cycloaddition reactions involving diazo compounds are particularly attractive because of their ability to rapidly construct densely functionalized azaheterocycles in a regioselective manner. In this context, the Bestmann-Ohira reagent has become a well-known reagent for the 1,3-dipolar cycloaddition reactions to produce phosphonylated heterocycles, besides its widespread use as a homologating agent for the conversion of aldehydes to alkynes. This account details our efforts toward broadening the synthetic utility of the Bestmann-Ohira reagent and related compounds for the preparation of azaheterocycles such as pyrazoles, spirooxindoles, triazoles, triazolines, and spiropyrazolines, emphasizing on domino multicomponent reactions employing readily available feedstock reagents.