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RACEMIC MODIFICATION (RACEMATE || RACEMIC MIXTURE): SEPARATION OF ENANTIOMERS-RESOLUTION

October 22, 2023 / By

An equimolar mixture of two enantiomers is called a racemic modification (or racemate or racemic mixture). When enantiomers are mixed together in equal proportion, the rotation caused by a molecule of one isomer is exactly canceled by an equal and opposite rotation caused by a molecule of its enantiomer. As a result, the racemic modifications …

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FISCHER FORMULA, FLYING WEDGE FORMULA, AND SAWHORSE FORMULA AND THEIR INTERCONVERSION

October 1, 2023 / By

FISCHER PROJECTION FORMULA: It is a two-dimensional depiction of an organic molecule at the tetrahedral carbon center. The four bonds at the tetrahedral carbon are represented by two vertical and two horizontal straight lines. The vertical lines are presumed to lie below the plane of the paper and the horizontal lines are presumed to lie …

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PART II: WEINREB KETONE SYNTHESIS: CARBON – CARBON BOND FORMATION USING WEINREB AMIDE AND ORGANOMETALLIC REAGENTS

September 24, 2023 / By

The synthesis of ketones from N-methoxy-N-methyl amide, called as Weinreb amide, using organometallic reagents is known as the Weinreb ketone synthesis. Generally, the direct conversion of acid chlorides or esters to ketones using organometallic reagents does not result in a high yield of ketones because the intermediate ketones are highly reactive towards the organometallic reagents …

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WEINREB AMIDE SYNTHESIS: PART I: WEINREB AMIDE PREPARATION

September 24, 2023 / By

The direct conversion of carboxylic acids or acid chlorides or esters to ketones or aldehydes using organometallic reagents usually does not result in high yield because the intermediate ketones are highly reactive towards the organometallic reagents. However, after derivatization of these carboxylic acid derivatives to the corresponding Weinreb amide, the reaction with organometallics does give …

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MIZOROKI-HECK REACTION: CARBON-CARBON BOND FORMATION CATALYZED BY PALLADIUM

September 10, 2023 / By

During the early 1970s Tsutomu Mizoroki and Richard F. Heck independently discovered that the reaction of aryl, benzyl, and styryl halides with alkenes at a high temperature in the presence of a hindered amine base and palladium catalyst resulted in the equivalent substituted alkenes. The Palladium-catalyzed arylation or alkenylation of alkenes is known as the …

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MIGITA-KOSUGI-STILLE COUPLING: STILLE CROSS-COUPLING REACTION: CARBON-CARBON BOND FORMATION

September 5, 2023 / By

In 1976, the first palladium-catalyzed cross-coupling of organotin compounds was accomplished by C. Eaborn, et al. The next year, M. Kosugi and T. Migita described the transition metal-catalyzed cross-coupling of organotin compounds with aryl halides and acid chlorides. Following this, in 1978, J.K. Stille used organotin compounds to synthesize ketones using milder reaction conditions than …

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BUCHWALD-HARTWIG CROSS-COUPLING REACTION: C-N BOND FORMATION

September 4, 2023 / By

Aryl amines and related heterocycles are essential components in natural products, pharmaceuticals, agrochemicals, and various other compounds. This significance has driven chemists to seek advanced methods for forming carbon-nitrogen (C-N) bonds efficiently. Historically, the formation of C(sp2)-N bonds has been achieved using nucleophilic aromatic substitution (SNAr) or Goldberg and Ullmann reactions. In 1983, Nigita and …

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WOHL-ZIEGLER BROMINATION: ALLYLIC AND BEZYLIC BROMINATION WITH N-BROMOSUCCINIMIDE (NBS)

September 5, 2023 / By

Introducing a bromine substituent at the allylic positions of olefins or at the benzylic positions of alkylated aromatic or heteroaromatic compounds is known as the Wohl-Ziegler Bromination reaction. The procedure utilizes N-Bromo succinimide (NBS) as a typical brominating agent in refluxing carbon tetrachloride (CCl4) in the presence of a radical initiator such as dibenzoyl peroxide …

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SUZUKI-MIYAURA CROSS-COUPLING REACTION: CARBON-CARBON BOND FORMATION

August 28, 2023 / By

Cross-coupling reactions occur when two reagents react together with a metal catalyst to form a new covalent bond. A cross-coupling reaction in organic synthesis occurs when two fragments are joined together with the aid of a metal catalyst. Cross-coupling has been an essential reaction in catalytic organic chemistry with the pioneering work by Heck, Negishi, …

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STORK ENAMINE SYNTHESIS: ALKYLATION OF ALDEHYDE OR KETONE

August 14, 2023 / By

An indirect method for the selective alkylation and acylation of an aldehyde or ketone is via an intermediate called ‘Enamine’. An enamine is an unsaturated compound derived from the condensation of an aldehyde or ketone with a secondary amine. Enamine can be compared with ‘Enol’. Enamines are considered to be nitrogen analogs of enols. Enamines …

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