Lecture 3- CC bonds

Question 1

Intermolecular C-C bond formation

Answer 1

RX + =-EWG -> R—EWG +Bu3SnX

attack is towards alpha (non ewg end)
v v sensitive to bulk on the a carbon

excess of alkene and slow addition of bu3SnH

rad on ewg C –> H (snbu3)

Question 2

2 main examples of intramolecular c-c bond formation

Answer 2

5-hexanyl and 6-heptanyl

Question 3

For 5 hexanyl radical TD and K

Answer 3

K = 5 ring plus a methyl group
TD = 6 ring
CYCLISATION UNDER KINTETIC CONTROL
K-ts- envelope and strain free - substituents always pseudoequatorial

Question 4

heterocycles via rad c-c intra

Answer 4

R2N(—B)(—=)

Normal conditions –> 5 prod etc etc

Question 5

For 5Hex- how do you get 6 to predominate

Answer 5

SUBS, EWG, triangle

1. substituent on alkene (kinda like aldehyde to ketone)
2. Stabilize rad end with EWG - rev reaction–> TD prod
   3.vinyl R2C(——-||-BR)(——=) low conc
   goes to cylcopropane attatched to the original ring and then opens up

Question 6

Why does 6-heptenyl work in the same way

Answer 6

slower
selectivity worse
h abstraction occurs 1- rad 5 on h
rad can be then stab by double bond via resonance

Question 7

Medium rings

Answer 7

ring expansions

see card

Question 8

macro rings

Answer 8

one end halogen, other end TERMINAL ALKENE ||

Question 9

Tandom

Answer 9

formation of several rings and cc bonds to be performed in a single operation

Question 10

Why is HSnBu3 bad

Answer 10

toxic,
smell
diff to seperate

Question 11

Alternatives

Answer 11

NaBH4 (Bu3SnX-> Bu3SnH)

HSi(SiMe3)3
si-h h stronger bond but si me3 groups more reactive only 1 order less reactive