Organic Chemistry: Reduction, Protection, and Reagent Strategies (Lecture Notes)

Vocabulary flashcards covering reagents, protecting groups, and key reactions from the lecture notes (reduction, oxidation, protection, cyanohydrin, imine/enamine formation, and esterification-related concepts).

LiAlH4

A strong hydride reducing agent that reduces most carbonyl compounds (aldehydes, ketones, esters, and carboxylic acids) to alcohols; reacts vigorously with water/ROH; incompatible with protic solvents.

NaBH4

A milder hydride donor that reduces aldehydes and ketones to alcohols; generally does not reduce esters or carboxylic acids under standard conditions; more tolerant of protic solvents than LiAlH4.

DIBAL-H

Diisobutylaluminium hydride; selectively reduces esters to aldehydes at low temperature (e.g., −78°C); does not typically reduce carboxylic acids under controlled conditions.

DIBAL-H (nitriles)

Under certain conditions, DIBAL-H can reduce nitriles toward aldehydes upon hydrolysis; provides a route to aldehydes from nitriles.

Grignard reagent (RMgX)

Organomagnesium reagent that adds to carbonyls to form secondary/tertiary alcohols after aqueous workup; highly reactive; reacts violently with water/air; must exclude -OH groups from substrates.

Organolithium reagent (RLi)

Highly reactive organometallic compound similar to Grignards (strong nucleophile/base); used to form carbanions and attack carbonyls; moisture- and air-sensitive.

TBDMSCl (tert-butyldimethylsilyl chloride)

A silyl-protecting group reagent that forms TBDMS ethers to protect alcohols; typically used with a base (e.g., imidazole) and later removed by fluoride or strong acid.

Imidazole

A base commonly used to activate silyl chlorides (like TBDMSCl) for alcohol protection; also serves as a mild nucleophilic catalyst in protection chemistry.

Wittig reagent

Phosphorus ylide used in the Wittig reaction to convert carbonyls into alkenes; yields E and/or Z alkenes; often gives a mixture of stereoisomers; not effective with amides/esters.

Wittig reaction (ylide formation)

Reaction that forms carbon–carbon double bonds from a carbonyl compound and a phosphorus ylide; requires generation of the ylide (often from Ph3P=CHR) and typically gives alkenes with defined stereochemistry when stabilized ylides are used.

Cyanohydrin formation

Condensation of an aldehyde or ketone with HCN (acid-catalyzed) to give a cyanohydrin; introduces a nitrile and a hydroxyl group on adjacent carbons.

Acetal

Protecting group formed from a carbonyl and two equivalents of an alcohol under acid catalysis; acetal is stable to base but cleaved by acid to regenerate the carbonyl.

Hemiacetal

Intermediate in acetal formation (one alcohol adds to a carbonyl); can be isolated in some cases but typically converts to acetal or reverts to carbonyl under reaction conditions.

Acetal protection group

General strategy to protect aldehydes/ketones as acetals during multi-step sequences; requires strong acid for formation and mild acid or specific conditions for deprotection.

Imine (Schiff base)

A carbon–nitrogen double bond formed by condensation of an aldehyde/ketone with a primary amine under mild acid; hydrolyzes back to the carbonyl under aqueous acid.

Enamine

Reaction product of a ketone/aldehyde with a secondary amine; enamine acts as an enolate equivalent for nucleophilic alpha-functionalization.

CBS reduction

Corey–Bakshi–Shapiro enantioselective reduction of ketones to chiral secondary alcohols using a chiral oxazaborolidine catalyst and borane; provides one enantiomer preferentially.

PCC oxidation

Pyridinium chlorochromate; mild oxidant that oxidizes primary alcohols to aldehydes and secondary alcohols to ketones without overoxidation.

Jones oxidation

Strong oxidation using CrO3/H2SO4; oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones; typically used in aqueous acetone medium.

Acyl chloride

Reactive carboxylic acid derivative (R-COCl); reacts with amines to give amides and with alcohols to give esters; typically prepared from carboxylic acids with reagents like SOCl2.

Anhydride

Carboxylic acid derivative formed by two carboxyl groups; reacts with nucleophiles to form esters or amides; can be less reactive than acyl chlorides but still versatile.

Fischer esterification

Acid-catalyzed condensation of a carboxylic acid with an alcohol to form an ester; equilibrium process requiring excess alcohol or removal of water to drive to products.

Intramolecular Fischer esterification (lactone formation)

Intramolecular version of Fischer esterification that forms lactones (five- or six-membered rings) efficiently under suitable conditions; accelerated by favorable ring size.

Ester hydrolysis (acid-catalyzed)

Acid-catalyzed cleavage of an ester to yield carboxylic acid and alcohol; water acts as the hydrolyzing agent; requires acid catalyst and heating.

Amide hydrolysis

Hydrolysis of amides to carboxylic acids and amines; typically acid- or base-catalyzed; amide carbonyl group is robust but cleavable under strong conditions.

Amide formation from acid chloride/amide formation

Formation of amides by reaction of acid chlorides with amines or other nitrogen nucleophiles; often requires base to neutralize generated HCl.

Carboxylic acid to alcohol reduction

Reduction of carboxylic acids to primary alcohols typically accomplished with LiAlH4; carbonyl oxygen is reduced to a hydroxyl and the acid moiety becomes an alcohol.

Esters to alcohol reduction

LiAlH4 reduces esters to primary alcohols; common method for converting esters to alcohols in organic synthesis.