Week 8

Question 1

hydrobromation details

Answer 1

step 1: BH3, THF (no intermediates!)
step 2: NaOH, H2O2
alkene fills B’s empty p orbital
one step to BH2 on less substituted C and H on other
b/c of transition state - more subbed C can better stabilize positive charge
ALWAYS SYN B/C OF TRANSITION STATE

Question 2

oxymercuration details

Answer 2

step 1: Hg(OAc)2 and H2O
step 2: NaBH4 (cleaves Hg-C and replaces Hg with H)
one step to 3 membered cyclic ring
be SUPER careful with stereochemistry of methyl group getting pushed back and forward by 3 membered ring and then water

Question 3

what 2 reasons account for hydroboration connectivity? why is it non-Markovnikov?

Answer 3

1. steric strain of methyl with B
2. in transition state, higher degree C better stabilizes positive charge

Question 4

hydrogenation

Answer 4

H2 gas
Pd/C (only alkenes)
syn

Question 5

carbene

Answer 5

CHCl3 in base -> CCl3(-) but chlorine is happier alone so -> CCl2

Question 6

simmon-smith

Question 7

hydroboration

Answer 7

1. BH3, THF
2. H2O2, NaOH

Question 8

oxymurcuration

Answer 8

1. Hg(OAc)2, H2O/THF (3 mem. ring, water attacks from opp. face)
2. NaBH4 (replaces C-Hg with C-H)

Question 9

halogenation in water vs THF vs. with NBS

Answer 9

both start with halonium ion formation. then,

a) THF - remaining halogen ion attacks from opp. face resulting in anti X’s

b) water - water attacks instead of halogen ion then depronated by another water to give an anti halogen and alcohol… BROMOHYDRIN

c) NBS - for example with Br2, it’s nasty so want to use NBS in H2O/DMSO

Question 10

hydration (not oxymercuration or hydrobromation)

Answer 10

add H2O (which becomes acid H3O+) and heat in H2SO4 catalyst

Question 11

3 types of hydration

Answer 11

water and heat with H2SO4 catalyst

Question 12

epoxidation

Answer 12

TRANS DIOLS
1. MCPBA (per benzoic acid O-O) makes 3 mem ring with O
2. acid like H3O+ in water

Question 13

dihydroxylation

Answer 13

SYN DIOLS
1. alkene nuc attacks O on OsO4, forms structure with entire OsO4
3. water breaks O-Os bonds and adds hydrogen onto O’s, NMO regenerates OsO4

Question 14

alkene cleavage

Answer 14

a) dihydroxylation then 1,2-diol cleavage
1. OsO4, NMO
2. HIO4 in H2O/THF (creates structure with HIO4 complex, electrons from one I-O bond create double bond to C and electrons from C-C bond create other C=O bond, that’s why it needs to be syn dihydroxylation and not anti epoxidation)

b) ozonolysis
1. O3
2. Zn/CH3COOH