final exam olefination rxns

witting rxn

aldhyde/ketone + (R)3P+ C- —> alkene and O=P(R)3

nonstabilized ylide

R groups: allkyl or H

cis oxaphosphate

Z alkene

semi-stabilized ylide

R groups: aryl, alkenyl, benzyl, allyl, H

E/Z mixture

stabilized ylide

R groups: -CO2R, -SO2R, -CN, -COR

trans oxaphosphate

E alkene

factors for nonstabilized ylides

concerted

irreversible

EWG on phosphorus

avoid Li base

factors for stabilized ylides

stepwise

reversible

use Li base/salts

no EWG on phosphorus

open TS

Schlosser Modification

favoring E alkene w/ non stabilized ylide

-make reversible

-use Li base/salt

-reprotonate w/ HCl —> forms trans 

-use K+ base —> triggers formation of oxophosphate and alkene

Horner Wadsworth Emmons

phosphonate ester + base + ketone —> alkene and phosphonate oxide

forming the phosphonate ester

arbuzov or perkov rxn

HWE mech steps

-base (NaH) removes a-H on phosphate ether

-forms enolate

-e- swings, enolate attacks aldehyde (reversible arrows **)

-O- attacks P, forms oxophosphate

-P=O forms, breaking into E alkene

Still-Gennari Mod of HWE

forms Z alkene

R1 group on phosphate ether is CH2CF3

mech is irreversible

Corey-Fuches rxn

aldehyde + CBr4/Ph3P (2 eq) —> dibromo olefin + nBuLi —> lithium acetylide + water —> terminal alkyne

Corey Fuches steps

-P removes Br from CBr4

-CBr3- attacks P

-Br- leaves in equilib

-2nd eq of PPhr grabs Br on carbon, e- make P=C

-P=C performs [2+2] w aldehyde

-bonds break to form P=O and alkene

-nBu attacks Br, adds Li in its place

-nBu removes H on alkene, forms Li alkyene

-C-Li bond grabs H in H2O, forms terminal alkyne

Seyferth-Gilbert rxn

aldehyde/ketone + N2 phosphate + base —> alkyne + N2

Seyferth-Gilbert steps

-nBu- removes H from N2 phosphate

-LP on carbon attacks carbonyl

-O- LP attacks P, forms oxophosphate

-P=O forms, generates alkene w/ N2 and R group

-H on alkene shifts to other carbon, kicks out N2 and generates alkyne

Julia-Lythgoe rxn

-alkylphenyl sulfone + base + ketone + carbonyl-X —> E alkene

Julia-Lythgoe steps

-nBu- removes H in alkylphenyl sulfone

-LP on C attacks ketone

-O LP from ketone attacks X-carbonyl

-O Lp swings, kicks out X

-SmI2 donates radical to a-carbon in sulfone, kicks out S group

-SmI2 donates another radical

-LP on C swings, forms alkene, kicks out carbonyl group

Sylvestre Mod rxn

Bt-sulfone + aldehyde —> E alkene

Sylvestre Mod steps

-LP on carbon of sulfone attacks aldehyde

-O- LP attacks carbon of bt group, e- swing to N

-N e- swing, break S bond to bt group

-O- LP swing, remove SO2, generate alkene

Takai-Utimoto rxn

aldehyde + CHX3 + CrX2 —> alkene

Takai-Utimoto steps

-carbon-Cr bond attacks carbonyl

-swaps to C-C bond, O- coordinates with Cr+

-other C-Cr bond breaks, e- swing to form alkene