Selectivity
Selectivity
Chemoselectivity Regioselectivity Stereoselectivity (Which) (Where) (How) Chemoselectivity
Preferential selectivity of one functional group over other
Two different functional groups and unequal reactivity
Reaction of one of two identical functional groups
1 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Reaction of a group once, when it may react again Selective Reduction: Chemoselective reduction of C=C over C=O: O O
H 2 /Pd
Chemoselective reduction of C=O over C=C: O OH
NaBH 4 , CeCl3
Chemoselective reduction of α,β-unsaturated ketones over allylic alcohols: O O OH O
2 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity
NaBH 4 , CeCl 3 EtOH, -15 oC
3 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity Selective Reduction: OH O O 1 NaBH 4 (0.25 eq) /3 BH 3
O O HO
Chemoselective reduction of alkenes over alkenones:
O ( PPh 3 ) 3 RhCl
H 2 , EtOH O
Chemoselective reduction of alkenones over alkenes:
4 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity K-Selectride O THF or MeCu, DIBAL-H O Chemoselective reduction of alkynes over alkenes: H 2 / Pd-CaCO 3 Quinoline
H 2 / Pd-CaCO 3 Quinoline
5 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity Chemoselective reduction of COOR over CN: CO2R CH2OH
Ca(BH 4 ) 2 MeOH CN CN Chemoselective reduction of α,β-unsaturated esters in presence of alkenes :
Mg, MeOH
EtOOC EtOOC
Chemoselective reduction of C=O over COOR:
6 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity HO C
NaBH 4 MeOH O CO2Me CO2Me O Clemmensen reduction
HO HO O O Chemoselective reduction of carboxylic acids in presence of esters, nitro and cyano groups:
7 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity O
HOOC THF O BH3, SMe2 HOH2C O O
Chemoselective reduction of amides in presence of esters: COOMeCOOMe 2 /3 BH 3. THF
N N O Selective Oxidation:
8 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity Chemoselective oxidation of allylic alcohols over other OH OH
MnO 2
HO CHCl 3 O alcohols:
Chemoselective oxidation of secondary alcohols over primary alcohols AgCO3, Celite : OH OH Benzene O OH OH NaOCl, AcOH O
9 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity
o H 2 O, 25 C OH OH Selective Oxidation: Chemoselective oxidation of lactols over other alcohols:
O O AgCO 3 , Celite OH Benzene O OH OH
Chemoselective epoxidation of allylic alcohols over unfunctionalized alkenes:
10 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity t -BuOOH O VO(acac) 2 OH OH Chemoselective epoxidation of α,β-unsaturated ketones over alkenes: O O KOH, H 2 O2
O
Chemoselective epoxidation of alkenes over α,β-unsaturated ketones:
11 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity
O m - CPBA DCM
O O Chemoselective acylation of amines over phenols:
NH2 NHAc
Ac 2 O (1 eq) Pyridine
OH OH
Chemoselective alkylation of phenols over carboxylic acids: 12 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity COOH COOH COO I Base
Acid O OH O
Reaction of One of Two Identical Functional Groups: Monoprotection of a diol: NaH, BnBr
HOOHHOOBn
Monohydrolysis of an ester: 13 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity
CO2Me (1) NaOH, MeOH (1 eq.) CO2Me
CO2Me (2) Acid CO2H
Reaction of A Group Once When It May React Again: Preparation of half esters:
OH OCOCl
COCl 2
Partial reduction of dinitro compounds:
14 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Chemoselectivity
NaSH, MeOH
NO2 NH2 NO2NO2
15 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Regioselectivity Preferential reactivity of one site over the other site of the same functional group Addition of HBr to alkenes: Br Br HBr HBr ( PhCOO ) O 2
Hydration of alkenes:
Ph Ph Ph OH OH BH 3 . THF (1) Hg(OAc )2
(2) NaBH 4
16 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Regioselectivity Hydration of alkynes: O (1) HgSO 4 (1) BH .THF 3 H 2 SO 4
CHO (2) NaOH, H2 O 2
Baeyer- Villiger Oxidation:
O CF3 CO 3 H O
Birch Reduction: OMe OMe COOH COOH
17 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Regioselectivity O Diels-Alder Reaction: R R O R
Li, NH 3 Li, NH3 + EtOH EtOH O
major minor
O O
18 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Regioselectivity R R
R O +
O major minor Diels-Alder Reaction: O O
O O OAc O O OAc H H
19 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan H H H Selectivity Epoxide Opening: Regioselectivity O Me OH H SO O OAc NaOMe O OAc O OAc H Ra Ni, H 2
O O SPh O O SPh O O
HO Me MeH 2 4 Me Me H Me OMe MeMe MeOH MeO Me Aromatic electrophilic substitution:
20 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Regioselectivity
HNO 2
H 2 SO 4 NO2
NO2 Friedel-
Crafts Reaction:
O
RCOCl, AlCl3
O O
21 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan Selectivity Regioselectivity
RCOCl, AlCl3
SiMe3
22 CH-423 Course on Organic Synthesis; Course Instructor: Krishna P. Kaliappan