Carbon-Carbon Bond Forming eactions Addition of Cyanide Nucleophiles S N 2 displacement N 2 X KCN CN C - X = I, Br, Cl, Ts, Ms - SN2 process reactivity? stereochemistry? - one carbon chain extension addition to aldehydes & ketones KCN ' ' Cl (aq) CN 3 + Δ ' C 2 - mechanism: nucleophile addition - reversible process (K)
Carbon-Carbon Bond Forming eactions Addition of Cyanide Nucleophiles S N 2 displacement N 2 X KCN CN C - X = I, Br, Cl, Ts, Ms - SN2 process reactivity? stereochemistry? - one carbon chain extension addition to aldehydes & ketones KCN ' ' Cl (aq) CN 3 + Δ ' C 2 - mechanism: nucleophile addition - reversible process (K)
Carbon-Carbon Bond Forming eactions Addition of Cyanide Nucleophiles S N 2 displacement N 2 X KCN CN C - X = I, Br, Cl, Ts, Ms - SN2 process reactivity? stereochemistry? - one carbon chain extension addition to aldehydes & ketones KCN ' ' Cl (aq) CN 3 + Δ ' C 2 - mechanism: nucleophile addition - reversible process (K)
Carbon-Carbon Bond Forming eactions Addition of Acetylide Anions S N 2 displacement X ' strong base ' - pka alkyne? - deprotonation requires strong base: Na, nbuli, LDA, MgX, NaN 2 - X = halogen or sulfonate addition to aldehydes & ketones ' strong base ' - propargyl alcohols are useful synthetic intermediates
Carbon-Carbon Bond Forming eactions Addition of rganometallic eagents to Carbonyl Derivatives addition to aldehydes & ketones 'MgX or 'Li ' - Grignard and organolithium reagents are highly basic - beware of acidic functionality (alcohols, carboxylic acids). - beware of other reactive FG (including protecting groups) addition to esters 'MgX or 'Li ' ' - introduction of 2 equivalents of MgX or Li - cannot stop at ketone stage except in special cases
Carbon-Carbon Bond Forming eactions Addition eactions of Cuprates epoxide opening 'MgX, CuI or ' 2 CuLi ' - addition of nucleophile to least hindered position mixtures can result - SN2 mechanism addition to acid chlorides ' 2 CuLi Cl ' - chemoselective addition to acid chloride in the presence of ketones, enones, and esters - aldehydes may react
Carbon-Carbon Bond Forming eactions Addition eactions of Cuprates conjugate addition ' 2 CuLi ' - regioselective 1,4-addition to enones and conjugated esters
Carbon-Carbon Bond Forming eactions Alkylation of Enolates malonic ester & acetoacetic ester syntheses 1. base, 'X 2. 3 +, Δ ' 1. base, 'X 2. 3 +, Δ ' - dicarbonyl derivatives show enhanced acidity; lower reactivity - pka malonic ester (?) vs acetoacetic ester (?) vs ketone (?) - deprotonate with weak base under thermodynamic conditions Na/ is typical; match base to ester addition to aldehydes & ketones 1. base ' 2. 'X - pka ketone? - direct deprotonation requires strong, non-nucleophilic base, e.g. LDA
Carbon-Carbon Bond Forming eactions Condensation eactions of Enolates aldol reactions Na or - symmetrical aldol: self condensation of aldehyde or ketones - deprotonation with weak base under thermodynamic conditions: Na, Na, Na - can isolate aldol or elimination products 1. LDA (1.05 equiv) 2. ' " ' " - mixed aldol: reaction of two different aldehydes and/or ketones - requires quantitative deprotonation of one carbonyl component (LDA) - low temperature reaction typically gives aldol product
Carbon-Carbon Bond Forming eactions Condensation eactions of Enolates Claisen condensation Na 1. base 2. ' ' - both symmetrical & mixed Claisen condensation reactions are known - excellent method for preparation of beta ketoesters - intramolecular Claisen known as a Dieckman condensation
Carbon-Carbon Bond Forming eactions Friedel Crafts eactions Friedel Crafts Alkylation 3 CCl C 3 AlCl 3 - electrophiles include halides, alcohols, olefins - cationic intermediate rearrangements of side chain possible - overalkylation is possible - deactivated benzenes and anilines do not react - must consider regioselectivity when using substituted benzenes directing effects: o/p or m (see handout) Friedel Crafts Acylation Cl AlCl 3 - intermediate electrophile will not rearrange - deactivated benzenes and anilines do not react - over acylation does not occur - consider directing effects as above
Carbon-Carbon Bond Forming eactions Wittig eaction Ph 3 P=C' ' - reaction of aldehydes and ketones with phosphorous ylides - excellent method for alkene synthesis - reaction of aldehydes to give 1,2-disubstituted olefins is cis selective (some exceptions)
Carbon-Carbon Bond Forming eactions Diels-Alder eaction C 2 Δ or C 2 2 C Lewis acid C 2 C 2 Δ or C 2 C 2 Lewis acid C 2 C 2 Δ or C 2 C 2 Lewis acid C 2 - best case: diene electron rich; dienophile electron poor - stereochemistry of both diene and dienophile is conserved - endo TS is favored