Chemistry of Carbonyl Compounds ucleophilic addition (1,2-add) / substitution Conjugate addition (1,4 add) obinson annulation (McM 23.12) Alkylation of enolate anions namines as enolate equivs. (McM 23.11) δ- δ+ lectrophile ucleophile alogenation of enols / enolates elated react. in nature
Chemistry of Carbonyl Compounds δ- δ+ lectrophile ucleophile ucleophilic addition / substitution Aldehydes / Ketones Addition reactions u ' ' u, ':, alkyl, aryl - ot good leaving groups u ' Acid catalyzed ' ' u- Better electrophile Weaker nucleophile u ' _ u ' Carboxylic acid derivatives Substitution u L u L - Good leaving groups L - L u May also be acid cat. - > -C > - > - 2 : alogen, :, alkyl, aryl
Aldehydes / Ketones Addition reactions The Cannizzarro reaction ydride as leaving group! u ' ' u, ':, alkyl, aryl - ot good leaving groups u ' + : o acidic α- ex -, -Ph. -Bu t 2 Aldehyde Carboxylic acid + prim. alcohol icotinamid adenine dinucleotide 2 2 P 2 P 2 - prim or sec. Alchohol dehydrogenase (AD cont.) aldehyde / ketone P = AD P AD Aldehyde dehydrogenase =Phosphate: ADP +, ADP
Conjugate Addition δ- δ- δ+ δ+ 1,2-addition u 1,4-addition (conjugate addition / MIchael addition) 1,2-addition, x: Alcohols rganolithium Identity of u Sterical factors 1,4-addition, x: Amines rganocuprates Termodyn. prod, Michael acceptor WG S C 2 S 2 Michael reaction ' ' B! resonance forms Well stabilized enolate anion '' '' ''
SAB theory (not in McM) SAB : ard and soft acids and bases Lewis bases / nucleophiles Lewis acids / electrophiles Donor atom - hard bases: high electroneg. low polarizability hard to oxidize Donor atom - soft bases: low electroneg. high polarizability easy to oxidize ardness F - > Cl - > - >I - F - > - > 2 - > C 3 - Acceptor atom - hard acid small high positive charge no unchared e- pair in valence shell high electroneg. low polarizability Acceptor atom - soft acid large low positive charge unchared e- pair in valence shell low electroneg. high polarizability ard acids prefer to bind to hard bases Soft acids prefer to bind to soft bases
ardest electrophilic site Softest nucleophilic site u Softer u u 1,4 addition arder u 1,2 addition But also Kin. / termodyn. control Steric shielding
obinson Annulation (McM 23.12) ' ' 1,5-diketone acidic α- Michael react. ing forming react. annulus (lat.) = ring Aldol condensation - 2
δ- δ+ lectrophile ucleophile nolate anion ucleophilic species (eact with hard + ) : - Alkyl halides - Carbonyl compounds (Aldol, Claissen condens.) - alides (eact. with soft + )
egioselectivity in enolate anion formation (not in McM) Acidic protons Kinetic control sterically hidered base Low temp termodynamic control
lectrophilic addition to conjugated dienes - sec, allylic cation 1,2-add. prod. kinetic prod. + prim. cat. 1,4-add. prod. termodyn. prod. Termodyn prod: igh activation barrier, most stable prod. Vigorous cond. (high temp), reversible Kinetic prod: Low activation barrier, less stable prod. Mils cond, (low temp,) irreversible
WG Michael acceptor WG nolizable S C 2 S 2 C 2 S 2 ca pka: 17 19 25 25 10 30 Alkylation of enolate anions : Strong, sterical hindrance Ketones, esters, nitriles (Aldehydes: condensation) - + n-bu-li Li + n-bu pka ca 40 Litium Diisopropyl Amide
Alkylation of 1,3-dicarbonyl compounds followed by decarboxylation - - + / 2 C + ' ' + / 2 - C 2 '
namines as enolate equivalents (McM 23.11, Lab ex. 11) Synthesis of enamines prim. amine - 2 2 - - ketone / aldehyde Iminium ion - Imine sec. amine ' ' ' ketone / aldehyde Iminium ion namine eutral imine
eactivity of enamines ' namine ' 2 2 ' ' + ' Alkylation (alkyl halides) Conjugate addition (Michael acceptors) Acylation (acid halides) Monoalkylation o strong base
alogenation of enolate anions -B eacts further in the presence of base and halgen source Fairly good leaving group C + 3 C 3 + pka =I: 14
alogenation of neutral enols - Aldehyde or ketone (acid, ester, amide - not enolization) 2 - mainly monohalogenated prod. + α-omination of acids P P Acid bromide generated in situ nolize more easily than acid 2 cf McM 17.7 - + P 3 - + P P- bond cf Wittig ell Volhart Zelinskii eact. Intro of Cl also possible 2
Carbonyl condensations in nature Acyl-CoA Acetyl-CoA (Acetyl co-enzyme A) 2 u 3 C S P P P 3 ature's Cl or Acetyl-CoA Choline Synthesis of Acetylcholine (neurotransmittor) Acetylcholine esterase S CoA Acetylcholine
Carbohydrates Degradation / oxidation of fatty acids CoA S + C 2 C 2 xaloacetic acid Aldol ydrol. Acyl-CoA 2 C C 2 Citrate cycle nergy C 2 Citric acid Degradation / oxidation of fatty acids S CoA S CoA Claissen condes. S CoA Metab. with little carbohydrates (Diabetes, starvation, diets) Acetone Acetoacetyl-CoA Biosynthesis Steroids, Lipids etc * +