Catalytic, StereoselectiveDihalogenation of...

Topic ReviewIevgeniia Kovalova

14. 04. 2016

Catalytic,StereoselectiveDihalogenationofAlkenes

Cresswell,A.J.;Eey,S.T.-C.;Denmark,S.E.Angew.Chem.,Int.Ed.2015,54,15642

2

Introduction

C C

X

R1

R2

R3

R4

C CR1

R2

R3

R4

Br Br C CR1

R2

R3

R4

BrBr

δ+

δ-

π-complex

C C

Br

R1

R2

R3

R4

Br

C C

X

R1

R2

R3

R4

Roberts,Kimball,jacs,1937,59,946Robinson,InstituteofChem.OfGreatBritainandIreland,1932

3S.A.Snyder, Z.-Y.Tang, R.Gupta, J.Am.Chem.Soc.2009,131, 5744–5745

Enantioselective alkenedihalogenation insynthesisofnaturalproduct

O

O

O

OH

MOMO MeMe

O

O

O

OH

MOMO MeMe

ClCl

OBH

OO

O

O

OH

HO MeMeClCl

(-)-napyradiomycin

chiral additive(4 equiv)

THF, rt, 1hthen Cl2CH2Cl2

-78 ˚C, 20 min

93%, 93.5:6.5 er(97.5:2.5 er after recryst.)

chiral additive

4S.A.Snyder, Z.-Y.Tang, R.Gupta, J.Am.Chem.Soc.2009,131, 5744–5745

O

O

O

OH

MOMO MeMe

ClCl

O

O

O

OH

MOMO MeMe

5K.C.Nicolaou, N.L.Simmons, Y.Ying, P.M.Heretsch, J.S.Chen, J.Am.Chem.Soc. 2011,133, 8134–8137

Cl

OHCl

Cl

OHClMe

Cl

OHClCl

63%, er=90.5:9.5 65%, er=72:28 81%, er=85.5:14.5

Enantioselective, catalyticalkenedihalogenation

R2

R1 OH

4-Ph(C6H4)ICl2 (1.6 equiv)

(DHQ)2PHAL (20 mol %)CH2Cl2 (0.05 M)

-78 ˚C

R1 OHCl

R2 Cl

N

MeO

ON N

H

Et

N

OMe

ONN

Et

H

(DHQ)2PHAL

Ph

I ClCl

4-Ph(C6H4)ICl2

Cl-agentcatalyst

7

EtO

O

OEt

O

Br Br

R Ar

unreactive Br+ sourse

EtO

O

OEt

O

Br Br

Me*L Br

δ+

δ−

R Ar

Br

Br

Chiral ligandL*

Br- sourseM Br

enantioenriched dibromides

EtO

O

OEt

O

Br Br

HO Ph HO PhBr

Br

O

O OHOH

2-NpNp-2

Np-2 2-Np

(1.5-2.0 equiv.) (20-100 mol%)

BrTi(Oi-Pr)3 (1 equiv)

2:1 MeCN/Tolrt, 12-60h

D.X.Hu, G.M.Shibuya,N.Z.Burns, J.Am.Chem.Soc. 2013,135, 12960–12963

OH

Br

Br

20 mol % of diol: 60%, ee=76%100 mol % of diol: 63%, ee=86%

OH

Br

Br


F

OH

Br

Br


Cl

OH

Br

Br


Br

Enantioselective, catalyticalkenedibromination

8D.X.Hu, G.M.Shibuya,N.Z.Burns, J.Am.Chem.Soc. 2013,135, 12960–12963

HO Ph

OH

BrTi(Oi-Pr)3+

EtO

O

OEt

O

Br Br

+

3 i-PrOH

EtO

O

OEt

O

Br Br

Ti O

∗

PhBrO

O

OH

∗

EtO

O

OEt

OTi O

PhBrO

O

∗

Br

Br

EtO

O

OEt

OTi OBrO

O

∗

Br

BrPh

HO Ph

Br

Br

O

O OEt

Br

OEt

Ti(i-PrO)3

+

δ+

δ−

9D.X.Hu, F.J.Seidl,C.Bucher,N.Z.Burns,J.Am.Chem.Soc.2015,137,3795−3798

R2

R3

HOR1

R2HO

NBS (1.05 equiv)ClTi(Oi-Pr)3 (1.1 equiv)

13 (10-30 mol %)

hexanes-20 ˚C, 4-12 h

N

O

O

Br

NBS

N

HOt-Bu

t-Bu

OH

PhPh

13

R3

ClR1

Br

(chiral catalist)

(S)(R)

PhHO

88%, ee=89%, cr >20:1

PhHO

94%, ee=89%, cr=8:1

PhHO

89%, ee=92%, cr=18:1

ClCl

Me

Cl

Br

Br

Br Me

Br

ClHO

86%, ee=94%, cr=6:1

Enantioselective, catalyticalkenechlorobromination

10

OH

BrMe

OTi

LnClBr

Me OTiLn

Cl

NBS, ClTi(Oi-Pr)3

20 mol%(R,S)-13

20 mol%(S,R)-13

OH OH

BrCl

Br Cl

(S)-perillyl alcohol95%, cr=17:1 88%, cr>20:1

OH

NBS, ClTi(Oi-Pr)320 mol% (R,S)-13

hex, -20 ˚C OH

BrCl

DMP, NaHCO3

BrCl

O

H

BrCl

Ph3P=CH2

(+)-bromochloromyrcene

11

Me Me

Me

OH

Me Me

OH

NBS, (1.05 equiv)BrTi(Oi-Pr)3 (1.10equiv)

13 (20 mol%)

hex, -20 ˚C

Br

MeBr

Me Me

Me

OH Me Me

OHBr

BrMe

NBS, (1.05 equiv)BrTi(Oi-Pr)3 (1.10equiv)

13 (20 mol%)

hex, -20 ˚C

74%, 92% ee

78%, 95% ee

Ph OHPh OH

ClCl

t-BuOCl (1.05 equiv)ClTi(Oi-Pr)3 (1.10 equiv)

13 (30 mol%)

hex, -20 ˚C61%, 90% ee

12

X XXX X X+

moleculardihalogen

separate halenium and halide equivalents

dihalogen equivalent

Dihalogenating Reagents

R2

R1 R3

R4 BrR2

R3R4

R1Br

1 2

1 + 2NaBr + 1/2 Na2[B2(O2)2(OH)4] 2 Na3BO3 + H2O

1 + ZnBr2 + Pb(OAc)4 2 + Zn(OAc)2 + Pb(OAc)2

K.W.Rosenmund,W.Kuhnhenn,Ber.Dtsch.Chem.Ges. 1923,56, 1262–1269T.Schlama, K.Gabriel, V.Gouverneur, C.Mioskowski,Angew.Chem.Int.Ed.Engl.1997,36, 2342–2344

NH

Br3

Et4N+ Cl3-

Mioskowski's reagentslow release of Cl2 on storage

[R4N]+[(X2)nX]-

13

X

acid H +

X

acid H

δ+δ−

acid Xδ− δ+

+

H

acid

X

+ acid

Xδ− δ+

base + X base Xδ−δ+

base +X

PTCorganic phase

aqueousor solid phase

substrate

X

Brønsted acid

Lewisacid

Lewisbase

Phasetransfer

Catalysisproblem

14

Brønsted acidcatalysis

Brønsted acidcatalyzedalkenedihalogenation usingseparateX+andX-sources

acid HX

X

acid H

δ+δ−

δ−

H

acid Xδ− δ+

+

XX2

acid H

-

-

R2R1

HR2R1X

acid

acid

XR1

XR2

X

H

δ+δ−

15


Brønsted acidcatalyzedalkenedihalogenation usinganX+reagentcombinedwithacomplexanionofthehalideasanX- sources

acid HX

X

acid H

δ+δ−

δ−

H

acid Xδ− δ+

+

R2R1

HR2R1X

acid

acid

X-MXnR1

XR2

X

H

δ+δ−

+ MXn

MXn

16


Brønsted acidcatalyzedalkenedihalogenation usingadihalogenequivalentasasinglereagent

acid HX

X

acid H

δ+

δ−δ−

R2R1

R2R1X

R1

XR2

X

X

X

acid H X

+

X2

acid H-

-

17

Lewisacidcatalysis

Lewisacidcatalyzedalkenedihalogenation usingseparateX+andX- sourses

acidX

X

acid

δ+δ−

H

acid Xδ− δ+

+

R2R1

R2R1X

acid

XR1

XR2

X

δ+ δ−

XX2

acid-

-

acid

18

Lewisacidcatalysis

Lewisacidcatalyzedalkenedihalogenation usingadihalogen equivalentasasinglereagent

acidX

X

acid

δ+

δ−δ−

R2R1

R2R1X

R1

XR2

X

X

X

acid X

+

acid-

-

X2

19

Lewisbasecatalysis

Lewisbasecatalyzedalkenedihalogenation usingseparateX+andX- sources

baseX

δ+ δ−

R2R1

R2R1X

R1

XR2

X

X

X

+

basebase

Xbase +

X2

base-

-

X-

20

Lewisbasecatalysis

Lewisbasecatalyzedalkenedihalogenation usingadihalogenequivalentasasinglereagent

baseX

δ+ δ−

R2R1

R2R1X

R1

XR2

X

X

X

+

base

base

Xbase +

X

XX2

base-

-X

21

PhaseTransferCatalysis

Cationicphasetransfer-catalized alkenedihalogenation

PTC

organic

aq. or solid

X3R1

R2 HR1

R2H

XX

PTC X

PTC XR1

XR2

X

+

PTC X3 M X+ M X3 PTC X+

(NR4+, PR4

+ )

Y.-M.Wang, J.Wu, C.Hoong, V.Rauniyar, F.D.Toste, J.Am.Chem.Soc. 2012, 134,12928–12931

22


Enantioselective halocyclization via chiralanionphasetransfercatalysis

Y.-M.Wang, J.Wu,C.Hoong,V.Rauniyar, F.D.Toste, J.Am.Chem.Soc. 2012,134, 12928–12931

Me

NH

O Ph

O

N Ph

Me Br"Br+" sourse (1.3 equiv)chiral catalyst (5 mol %)

Na3PO4 (4.0 equiv)p-xylene/hex

(1:1 v/v, 0.025 M)

N NC6Me5

Br NNC6Me5

(BrF4)3

"Br+" sourse (i-Pr)3Si

(i-Pr)3Si

OO P

O

OH

i-Pr

i-Pr

i-Pr

i-Pr

i-Pri-Pr

chiral lipophilic catalyst

(precursor to chiral PT catalyst)

82%, 94% ee

23


Enantioselective halocyclization via chiralanionphasetransfercatalysis

W.Xie, G.Jiang, H.Liu, J.Hu, X.Pan,H.Zhang, X.Wan, Y.Lai, D.Ma, Angew.Chem.Int.Ed. 2013,52,12924–12927

"Br+" sourse (1.3 equiv)chiral catalyst (10 mol %)

Na3PO4 (4.0 equiv)p-xylene/hex

(1:1 v/v, 0.025 M)

N N Br

"Br+" sourse(i-Pr)3Si

(i-Pr)3Si

OO P

O

OH

i-Pr

i-Pr

i-Pr

i-Pr

i-Pri-Pr

chiral lipophilic catalyst

quantit., 95% ee

NTs

NHCO2Me

NTs

N

Br

HCO2Me

CF3

F3C

24

PTC

organic

solid

R1R2 H

R1R2H

X

PTCR1

XR2

X

+N

N

XX

R

X

N

NR

PTC

N

NR

PTCN

N

XX

R

+

N

NR

XPTCN

NR

+

N

NR

X X X


Anionicphasetransfer-catalyzedalkenedihalogenation

25

RR

XR H

H RX

X XC2h

C2

R

X

X

R

Cs

(homotopic termini)

(achiral)

RX

R RH H

X

X XC2v

Cs

(enantiotopic termini)

Ra b

R

X

X

R

C2

(enantiomers)

R

X

X

Ra

b

R2R1X

Cs

R1 HH R2

X

X X

C1

R1

X

X

R2

C1(constitutionallyheterotopic termini)

(enantiomers)

a b

R1

X

X

R2

a

b

R1X R1 R2

H HX

X X

C1

R1

X

X

R2

C1(constitutionallyheterotopic termini)

(enantiomers)

a b

R1

X

X

R2

a

bR2

Cs

(Enantiodetermining stepshighlightedwithboldarrows)

Symmetry-basedalkenedihalogenation via haliranium ions

chiral

achiral chiral

chiral

26

R1R2

X

R1 HH R2

a b

R1 HH R2a b

X

(racemization)

Cat*, Xfast

Cat*, X

slow

R1

XR2

X

R1

XR2

X

X

X

R1R2

X

R1 HH R2

a b

R1 HH R2a b

X

(epimerization)

fast

slow

R1

XR2

X

R1

XR2

X

Cat*, X

Cat*, X

Cat*

Cat*

X

X

Dynamickineticresolution(withsubstrate- orcatalyst-controlledhalideattackatcarbon“a”

Dynamickineticasymmetrictransformation(type1)(withsubstrate- orcatalyst-controlledhalideattackatcarbon“a”

Enantiodetermining nucleophilicattackofhalideionbykineticresolutionofhalenium ions

27

R1R2

X

R1 HH R2

a b

R1 HH R2a b

X

(racemization)

Cat*, X

attack at a

Cat*, X

attack at b

R1

XR2

X

R1

XR2

X

X

X

homomeric

Enantiodetermining nucleophilicattackofhalideion

Regiodivergent (enantioconvergent)reactionofaracemicmixture

28

Enantiodetermining haliranium ionformation

Forhaliranium ionformationtobeenantiodetermining,twoconditionsmustbemet:

1) thehalenium iontransfertotheolefinfromthe“X+”sourcemustbeirreversible

2) thehaliranium ionthusproducedmustbeconfigurationallystablepriortoitsnucleophilictrapping(itmustnotracemize).

R1 HH R2

XCat*

180 ˚

R1 HH R2

AuL*

180 ˚

R1 HH R2

OsO Cat*O

O O

Difficulttopredictstereochemical

informationvia σ∗orbital

Au(I) complexeshavelinearcoordination

geometry

Accesstoπ∗ orbitalallowstohavebetter

sterechemicalinteractionbetweenCat*andalkene

29

HH

HH

Br HHH H

free

HH

HH

Br HHH H

π-complex

HH

HH

Br

HHH H

transition state

HH

HH

Br

HHH H

π-complex

HH

HH

HHH H

free

Br

Alkene-to-alkene bromiranium iontransfer

30

Alkenedihalogenation withmaingrouphalidesasreagentorcatalysts

GroupIIIa (B,Al,Ga,In,Tl)Halides

C3H7C3H7

TiCl3•H2O (1 equiv)

CCl4, reflux C3H7C3H7

ClCl + C3H7

C3H7

ClCl

80 : 20

5% combined yield (w.r.t. TiCl3)(plus 33% of hydrochlorinated products)

anti-adduct syn-adduct

R1R2

X YH R2

R1 H

YX

π-complex

H R2R1 H

X

Xhaliranium

ion

HR2

R1 H

X

X

β-halocarbocation

or+X

-Y

X

H R2R1 H

YX

X

R1

XR2

X

-YR1

XR2

X

31


GroupIVa (C,Si,Ge,Sn,Pb)Halides

OnlyPbCl4 haspowertodichlorinate alkenes.Cl

ClCl

+

quant(w.r.t. PbCl4)

no yield given

Pb(OAc)4 (1 equiv)dry HCl (excess)

DCM-40˚C to -25˚C

P.W.Henniger, E.Wapenaar, E.Havinga,Rec.Trav.Chim.1966,85, 1177–1187

R1R2

X YH R2

R1 H

YX

π-complex

H R2R1 H

X

X

haliraniumion

HR2

R1 H

X

X

β-halocarbocation

or+X

-Y

X

H R2R1 H

YX

X

R1

XR2

XR1

XR2

X

-Y

32


GroupIVa (C,Si,Ge,Sn,Pb)Halides

Difluorination

AcO

Me H

Me COMe

H HAcO

Me H

Me COMe

H H

F F

Pb(OAc)4HF

DCM, -75˚C15 min

27%, (73% brsm)

R1R2

LnMX2

concertedgroup transfer

Type IVH R2R1 H

X XMLn

R1

XR2

X

-MLn

33


GroupVa (N,P,As,Sb,Bi)Halides

Nitrogen

ClClNCl3 (1 equiv)

0-5 ˚C

92%(w.r.t. NCl3)

J.W.Strand, P.Kovacic,Synth.Commun.1972,2, 129–137

34



Phosphorus

PhPh

PCl5 (2 equiv)

PhCl124 ˚C, 12h

PhPh

Cl

Cl

PhPh

Cl

Cl

+

85% 13%anti- syn-

PCl5 (1 equiv) Cl

Cl

Cl

Cl+

(2 equiv) "ionic" "radical"

With CHCl3 at 65 ˚C: 99 : 130 : 70With CCl4 at 65 ˚C:

35

MeMe

SbCl5 (1 equiv)

CCl473 ˚C, 10min

MeMe

Cl

Cl

MeMe

Cl

Cl

+

18 82:

96% combined (w.r.t. SbCl5)anti- syn-

MeMe

SbCl5 (1 equiv)

CCl476 ˚C, 10min

ClMe

Cl

Me

ClMe

Cl

Me

+

16 84:

98% combined (w.r.t. SbCl5)anti- syn-

(2.8 equiv)

(1.8 equiv)



Antimony

36

SbClCl

Cl

Cl

Cl

2Cl

Cl

Cl

Cl

Cl

ClSb

Cl

Cl

Sb

Cl

Cl

Cl

Cl

Cl

ClSb

Cl

Cl

ClCl

Cl

Cl

Sb

EquilibriaofSbCl5inCCl4


Antimony

R2R1

H R2R1 H

Cl ClSb

H R2R1 H

Cl

Cl5Sb Cl

SbCl5

[SbCl4]+[SbCl6]-

R1

Cl

Cl

R2

R1

Cl

Cl

R2

Cl3Sb

37


GroupVIa (O,S,Se,Te,Po)Halides

SulfurSO2Cl2

Initiator R

SO2Cl

RCl SO2

Cl

Cl R1R2

R1R2

Cl+

R1R2

ClSO2Cl2+

-SO2

R1R2

Cl

Cl

R1R2

Cl

O SO

Cl-Cl -SO2

SO2Cl2 (1 equiv) Cl

Cl

Cl

Cl+


At 76 ˚C: 12 : 8875 : 25At 76 ˚C with 1,3-DNB (0.2 equiv):

CCl4, 2h

79 : 21At 25-35 ˚C with SiO2 (1.8 equiv):

38


GroupVIa (O,S,Se,Te,Po)Halides

Sulfur SO2Cl2 (1 equiv) Cl

Cl

Cl

Cl+


At 76 ˚C: 12 : 8875 : 25At 76 ˚C with 1,3-DNB (0.2 equiv):

CCl4, 2h

79 : 21At 25-35 ˚C with SiO2 (1.8 equiv):

R1R2

X YH R2

R1 H

YX

π-complex

H R2R1 H

X

Xhaliranium

ion

HR2

R1 H

X

X

β-halocarbocation

or+X

-Y

X

H R2R1 H

YX

X

R1

XR2

X

-YR1

XR2

X

39


GroupVIIa (F,Cl,Br,I)Halides(exceptdihalogens)

Iodine

PhICl2

Cl PhI

Clheat or hν

Ph(Cl)I

Cl R1R2+ R1

R2

Cl

R1R2

ClPhICl2+

-PhIR1

R2

Cl

Cl

Cl+

40

PhMe

PhMe

PhICl2, hν

DCM, rt

ClHPh H

Me(fast)

ClHPh Me

H

ClICl

PhClICl

Ph

PhMe

Cl

ClPh

MeCl

ClFrom trans- 92 : 8From cis- 91 : 9


GroupVIIa (F,Cl,Br,I)halides(exceptdihalogens)

Iodine

41

R1R2

R1R2

Cl

Cl IPh

R1R2

I

Cl

PhCl

Type I -PhIR1

R2

Cl

Cl

-PhI R1R2

Cl

I ClPh

-PhI

R1R2

Cl

Cl

-PhI

Type IIinv

Type IIref



Iodine

Possiblereactionpathwaysfortheionicdichlorination ofalkeneswithPhICl2

42

HF

F

F

IMe δ+

δ−

R1R2

- HF R1R2

ITol

F

F

R1I

F

F 4-Tol

R2F

- 4-Tol- F-

R1

F

R2

F

MeO2C MeO2C

4-TolIF2 (1.3 equiv)

DCM/Et3•5HF (1/1 v/v)0˚C, 3h

55%



Difluorination

43

MeMe

MoCl5 (1 equiv)

CCl474 ˚C, 20min

MeMe

Cl

Cl

MeMe

Cl

Cl

+

8 92:

85% combined (w.r.t. MoCl5)anti- syn-

MeMe

MoCl5 (1 equiv)

CCl474 ˚C, 20min

ClMe

Cl

Me

ClMe

Cl

Me

+

15 85:

92% combined (w.r.t. MoCl5)anti- syn-

(35 equiv)

(25 equiv)

Alkenedihalogenation withtransitionmetalhalidesasreagentorcatalysts

GroupVI(Cr,Mo,W,)metalhalides

Molybdenum

44

R2R1

H R2R1 H

Cl ClMo

H R2R1 H

Cl

Cl5Mo Cl

MoCl5

[MoCl4]+[MoCl6]-

R1

Cl

Cl

R2

R1

Cl

Cl

R2


GroupVI(Cr,Mo,W,)metalhalides

Mechanismfortheformationofsyn- andanti-dichlorination products

45


GroupVII(Mn,Tc,Re,)metalhalides

Manganese(VII)

C4H9C4H9

C4H9C4H9

C4H9

ClC4H9

Cl

C4H9

ClC4H9

Cl

KMnO4 (1 equiv)BnNEt3Cl (1 equiv)Me3SiCl (4 equiv)

DCM, 0˚C to 20˚C


DCM, 0˚C to 20˚C

94%

81%

R1R2

Cl [Mn]H

Cl

R1 HR2

[Mn]H

Cl

R1 HR2

[Mn]

Cl

-[Mn]

Cl

R2HCl

R1H

46


GroupVII(Mn,Tc,Re,)metalhalides

Manganese(III)and(IV)

C3H7Me

C3H7

ClMe

Cl


DCM, 0˚C to 20˚C

95%, 64:36 dr

R1R2

Cl MnIII MnII

R1

ClR2

Cl MnIII MnII

R1

ClR2

Cl

MnO2 (1.5 equiv)Me3SiCl (6 equiv)

THF, 40˚C to 60˚C+Cl

Cl

ClCl

85% 8%

R1R2 Cl MnIV

R1

ClR2 R1

ClR2

Cl

Cl

Cl MnIII

-MnII

47

R1R2

[PdII] ClR1

R2

Cl

[PdII]

R1R2

Cl

[PdII]

or

syn anti

Known

R1 R2

[PdII] "Cl+" or "Cl-" + [O]

R1 R2

[PdII]

R1 R2

[PdII]or

Unknown

R1R2

[PdII] Cl

"Cl+" or "Cl-" + [O]R1

R2

Cl

ClR1

R2

Cl

Clor

syn anti

retentive invertive


Group10(Ni,Pd,Pt,)metalhalides

Palladium

48

BuPdCl2(PhCN)2 Bu

[PdII]

p-benzoquinoneLiCl, AcOH,rt Bu

ClCl

(no yield or dr published)


HO OH Pd(II)

[PdII]

X-, PBQ

[PdII]O

O

O

O

Pd0

Y-

XY

2H+

J.-E.Bäckvall, C.Jonasson,TetrahedronLett. 1997,38, 291–294

BuPd(OAc)2

p-benzoquinoneLiBr, AcOH,rt

BuBr

Br

(58%)

49

Thankyouforyourattention!

50

R1R2

X YH R2

R1 H

YX

π-complex

H R2R1 H

X

Xhaliranium

ion

HR2

R1 H

X

X

β-halocarbocation

or+X

-Y

X

H R2R1 H

YX

X

R1

XR2

X

-YR1

XR2

X

51

R1R2

LnMX2

anti-addition of M-X

H R2R1 H

M

π-complex

LnX

X

H R2R1 H

M

X

X Ln

-iranium ion

or M

XHR2

R1

HX

Ln

R1 HH R2X

X MLn

anchimericallyassisted

XH

R1H

R2MX

Ln

concerted

or R1

XR2

XType IIret

(retentive C-Xbond formation)

Type IIinv(invertive C-X

bond formation)

M

XHR2

R1

HX

Ln

X

R1

XR2

X

-MLn

SN2

-MLn

52

R1R2

LnMX2

syn-addition of M-X

H R2R1 H

4−membered transition state

MH

R1

XLn

H HR1 R2

X

X MLn

anchimericallyassisted

R1H

MX

Ln

concerted

or R1

XR2

XType IIIret

(retentive C-Xbond formation)

Type IIIinv(invertive C-X

bond formation)

M XH R2R1 H

XLn

X

R1

XR2

X

-MLn

SN2

M XXLn X

HR2

X

R2H

-MLn

53

R1R2

LnMX2

concertedgroup transfer

Type IVH R2R1 H

X XMLn

R1

XR2

X

-MLn

R1R2

"X "

X atom transferType V

R1R2

X

β-halo radical

R1R2

X

X Y

X Y -YR1

R2

X

X

chain reaction if Y•=X• or Y•→X• + Yʹ

RadicalTypeV

Catalytic, StereoselectiveDihalogenation of...

Documents

Transcript of Catalytic, StereoselectiveDihalogenation of...