Uses: Ar N 2 Ar N 2 Ar N Ar N 2 eduction Boron based reagents NaB 4 / NiCl 2 2 Ar C N Ar C N 2 Preparation: Zn(B 4 ) 2 ZnCl 2 (Ether) NaB 4 Zn(B 4 ) 2 Good for base sensitive groups Chelation control model C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Boron based reagents Zn(B 4 ) 2 1 2 2 Zn 2+ B 1 2 1 Zn(B 4 ) 2 Et 2 Me Zn 2+ Me Zn 2+ C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Boron based reagents NaB(Ac) 3 ; Me 4 NB(Ac) 3 C Bu 4 NB(Ac) 3 Ph C Bu 4 NB(Ac) 3 Ph Ac B Ac Ph Na + (Ac) 3 B - ipr Ac B Ac C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
Selectrides: eduction Boron based reagents Alkyl Borohydrides M B 3 M + = Li (L-Selectride) = K (K-Selectride) Me L- Selectride TF Me 1 2 L- Selectride TF 1 2 K- Selectride K- Selectride TF Br C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
LiBEt 3 (Superhydride): eduction Boron based reagents Alkyl Borohydrides Very reactive hydride source educe ketones, aldehydes, esters, epoxides and C-X bonds Br LiEt 3 B Br LiEt 3 B LA 73% LiEt 3 B 100% C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Boron based reagents Comparison between Borohydride and Boranes Borohydrides Negatively charged Nucleophilic Valence shell of boron completed octet ydride transfer occurs intermolecularly Boranes Neutral Electrophilic Boron contains six electrons and a vacant p-orbital ydride transfer occurs via a Lewis acid-base complex C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Ø LiAl 4 Ø Li( t Bu) 3 Al Ø ed-al Ø Al 3 Ø DIBAL- Lithium aluminum hydride (LiAl 4 ) Very powerful reducing reagent Available as either powder or pallet Used as a suspension in ether or TF eacts violently with water, alcohol educes carbonyl, carboxylic acid & ester educes nitrile, amide & aryl nitro group to amine educes acetylene to olefin educes C-X bond, opens epoxide C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Mechanism: Li Al ' ' Li C Al 3 ' ' ' Li Al N ' ' C 4 N 2 ' C ' ' C 2 N 2 N 2 C 3 N C 2 N 2 C N C 2 N 2 C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Alkyl halides: eduction of alkyl halides go via radical mechanism This is proved by- X e X X + X + e LA I 81% Alkynes: It is complementary to that of partial hydrogenation 2 /Pd CaC 3 LA C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
Epoxides: eduction eduction LA LA Axial attack LA 10 90 L-Selectride 93 7 C 2 Me C 2 Me LA C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction C C 2 EASY C C CCl C 2 Lactone Diol Epoxide Alcohol Ester Alcohol Carboxylic acid Alcohol Carboxylate Salt Alcohol Amide Amine Nitrile Amine DIFFICULT C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Alane (Al 3 ) Preparation: AlCl 3 + LA Al 3 + 3LiCl It is inert to olefin & nitro group Br Me Al 3 Br Ph LA Ph Al 3 1,2- selective Ph C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Diisobutylaluminium ydride (DIBAL-) Al ighly pyrophoric Al(i-Bu) 2 DIBAL- Work up CEt DIBAL- C 2 Under carefully controlled conditions, will partially reduce an ester to an aldehyde C 2 Me C Me Al If complex is Unstable If complex is Stable Fast C C 2 C C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan
eduction Direct conversion of acids to aldehydes: TMSCl DIBAL- Et 3 N TMS DCM, -78 o C Acid chloride to aldehyde using Weinreb s amide: Cl N Me Me N Me Me Weinreb's amide DIBAL- MgBr N Me Al Me C C- 423 Course on rganic Synthesis; Course Instructor: Krishna P. Kaliappan