Chapter 20 The carbonyl can be an electrophile, it can be attacked. It can occur under basic or acidic conditions.
Basic Conditions: H O 1. Nu- O
2. H2O workup Nu Nu:
HOH O :
Nu
Acidic Conditions: H+ H O : 1. H+, Nu: O
Nu
H + O OH
Nu Nu:
Hydride reductions. Basic conditions, H- is the nucleophile Ketones and aldehydes react w/ LiAlH4. H O 1. LiAlH4 O
2. H2O workup - H H:
HOH O :
H Esters and acid chlorides react w/ LiAlH4. H O 1. LiAlH4 O 2. H O workup OMe 2 H - H H:
HOH O : O O :
OMe H H H - H H: There are many sources of hydride with various reactivities Hydride Aldehyde Ketone Ester Amide Carboxyllic Acid Donors acid/ acid salt halide LiAlH4 Alcohol Alcohol Alcohol Amine Alcohol Alcohol LiAlH(OtBu)3 Alcohol Alcohol Alcohol - (too slow) N.R. Aldehyde NaBH4 Alcohol Alcohol N.R. N.R. N.R. ? NaBH3CN Alcohol N.R. N.R. N.R. N.R. ? DIBAL-H Alcohol Alcohol Aldehyde * Aldehyde* Alcohol ? * Stoichiometry must be carefully controlled. H2, Pd/C reacts preferentially with carbon-carbon double bonds.
Carbon Nucleophiles: - Both of the following create reagents that act like CH3 . EtBr + 2Li →EtLi + LiBr EtBr + Mg → EtMgBr
Alkyne nucleophiles. - + CH3C≡CH + NaNH2→ CH3C≡C: Na + NH3 - + CH3C≡CH + CH3Li → CH3C≡C: Li + CH4↑
CH3C≡CH + CH3MgBr → CH3C≡CMgBr + CH4↑
Ketones and aldehydes react w/ these carbon nucleophiles. H O 1. H3C CCMgBr O
2. H2O workup - C CH3CC: C CH HOH 3 O :
Esters and acid chlorides react w/ these carbon nucleophiles. H O 1. CH3Li or CH3MgBr O
2. H2O workup CH OMe 3 CH - 3 H3C:
HOH O : O O :
OMe H CH3 CH3 H3C - H C: 3
Grignards react with carbon dioxide to for carboxylic acids.
H O 1. CH3MgBr O C O 2. H2O workup H3C O - CH3: HOH O :
H C O 3 Cuprates are another source of carbon anions but they react differently then the carbon nucleophiles we have seen before. In enones they react at the 4 position and they can react with alyls halides including vinyl and aryl halides
Preparation 2MeLi + CuI → Me2CuLi
O H3C OH 1. CH3MgBr 1,2 addition
2. H2O
O O
1. (CH3)2CuLi 1, 4 addition
2. H2O workup H3C
O
H C 3
Cuprates can substitute alkyl groups for halogens (primary) which is no big deal but they can also do it with vinyl and aryl halides!!
(CH ) CuLi H C Br 3 2 3
(CH ) CuLi H C Br 3 2 3
Alkyl anions can react with epoxides. 1. CH MgBr O 3 OH
2. H2O workup
O
H C 3
Br MgBr OH
OH Br
Chomium(VI) reagents oxidize alcohols to ketones. (p434)
OH O
+ HCrO3-
O O H O Cr OH O
Primary alcohols and aldehydes are oxidized to carboxylic acids
OH O H O H2O OH H2CrO4 OH H2CrO4 H OH
Silver(I) will oxidize aldehydes to carboxylic acids. O O Ag2O H OH NH4OH