Named Reactions Flashcards
Wittig Reaction
General: Carbonyl + Phosphorous Ylid → alkene with ylid R group and carbonyl R groups
Mechanism: The negative charge of the ylid attacks the base of the carbonyl, pushing the pi electrons onto the oxygen. Then The oxygen attacks the positively charged atom of the ylid forming a four-membered ring. The bond between the oxygen and carbon breaks at the same time the phosphorous-carbon bond breaks forming a carbon-carbon double bond with a side product of oxygen triple bonded to phosphorous.
Stereochemistry: E isomer usually preferred over Z
Generating Phosphorous Ylids
General: Alkyl Halide + :PPh3 → Phosphorous ylid with the halide kicked out and the ylide deprotonated
Mechanism: The :PPh3 performs an SN2 with the alkyl halide kicking out the halide. The carbon attached to the phosphorous is then deprotonated by a strong base creating a carbanion
Corey-Chaykovsky Reaction
General: Essentially a Wittig Reaction with a Sulfonium Ylid–Carbonyl + Sulfonium ylid → epoxide with carbonyl and sulfonium ylid’s R group(s)
Mechanism: The negatively charged carbon attacks the base of the carbonyl, pushing the pi electrons onto the oxygen. The negatively charged oxygen then attacks the carbon joined to the sulfur kicking out S(Me)2 as a LG, forming an epoxide.
Generating Sulfonium Ylids
General: Alkyl halide + S(Me)2 → Sulfonium ylid with the halide kicked out and the ylide deprotonated
Mechanism: S(Me)2 performs an SN2 with the alkyl halide kicking out the halide. The carbon attached to the sulfur is then deprotonated by a strong base creating a carbanion
Wolff Kishner Reduction
General: Carbonyl + a nucleophile with two heteroatoms bonded → carbonyl is replaced with a double bond to a heteroatom and the rest of the nucleophile. And if subsequently treated with a strong base and temperature, the heteroatom and nucleophile is kicked out and replaced with two hydrogens
Mechanism: First few steps are identical to imine formation from a carbonyl (heteroatom–usually nitrogen double bonds where the oxygen of the carbonyl was). A base then keeps deprotonating the adjacent heteroatom, until a double bond is created between the two hetero atoms and the adjacent heteroatom has a negative charge. The negative charge moves from the heteroatom to form another bond between the heteroatoms kicking out the group leaving a negative charge on the carbon. Necessary proton transfers through which are solvent mediated
Aldol Condensation Reaction
General: Two keytones/aldehydes (the same or different) react, creating a new carbon-carbon bond. Then an H2O group leaves forming an alkene (base deprotonation or acid catylization)
Mechanism: An alpha hydrogen is deprotonated by a base making a carbanion which acts as a nucleophile attacking the base of the carbonyl on the other molecule, pushing the pi electrons to the oxygen, which then becomes an OH group after a proton transfer. If still in a basic solution a subsequent deprotonation occurs on the alpha hydrogen closest to the hydroxy group, creating an alkene, pushing the carbonyl pi electrons onto the oxygen. The negatively charged oxygen reforms the double bond spontaneously pushing the alkene onto the next carbon over, kicking out an OH group. If acid catalyzation is used instead, then the OH group protonates and becomes H2O. The conjugate base of the acid then deprotonates the alpha hydrogen closest to the water group performing a simple E1 elimination kicking out the water.
Horner Wodsworth Emmons Reaction
General: A specific phosphorous based ylid is deprotonated by H- which then attacks the aldehyde/ketone → a Wittig alkene product with an EtO group attached to the aldehyde/ketone’s R groups
Mechanism: Works exactly like a Wittig Reaction: the ylid is deprotonated to achieve a negative charge on the carbon attached to the phosphorous. The negatively charged carbon then attacks the base of the carbonyl of the aldehyde/ketone, pushing the pi electrons onto the oxygen. The negatively charged oxygen then attacks the phosphorous creating a four-membered ring. The ring spontaneously breaks, creating an alkene with a carbonyl and EtO group (both from the ylid) and the R groups from the aldehyde/ketone. A side product from the ylid reminisce and the oxygen of the aldehyde/ketone is also produced
Arborov Reaction
General: Essentially a Wittig Ylid synthesis. Phosphorous attached to three OEt groups + alkyl halide with a carbonyl and an OEt group → Ylid
Mechanism: The phosphorous attacks the carbon with the halide, kicking it out. The negatively charged halide then attacks the first carbon of one of the OEt groups, kicking out the whole ylid and forming a side product of Me-C-Br
Robinson Annulation
General: A deprotonated alpha carbon does a 1, 4 addition to another carbonyl, followed by a self aldol condensation → product with an alkene and a carbonyl
Mechanism: A carbonyl’s alpha carbon is deprotonated and then performs a 1,4 (Michael) addition to another carbonyl. A base is then introduced, deprotonating an alpha carbon, leading to a self-aldol reaction which usually results in 5 or 6 membered rings. A proton transfer step occurs, only for the base to deprotonate the hydrogen next to the OH group, which performs an E2 reaction, kicking out the OH group and forming a double bond.
Mannich Reaction
General: Aldehyde/ketone + amine (acidic)→ imine formation. Imine + aldehyde/ketone (basic then acid w/up) → product through acting like an aldol reaction with imine as the electrophile
Mechanism: Imine formation followed by imine aldol reaction. After the imine is formed, an aldehyde/ketone is deprotonated by a base. The carbanion then acts like a nucleophile attacking the carbon attached to the nitrogen of the imine in an aldol-like reaction (with necessary proton transfers from solvent).
Gabriel Synthesis
Hell-Vollhardt-Zelinskii Reaction
Bayer-Villiger Reaction
Claison Condensation
Deckman Reaction
