Heterocycles

Question 1

Pyrrole reactivity

Answer 1

Electron rich, N lp part of aromatic system, activated towards electrophilic attack

Question 2

Pyridine reactivity

Answer 2

Electron poor, N lp not part of aromatic system, electronegative N lowers HOMO and LUMO, deactivated towards electrophilic attack, basic N

Question 3

Oxazole retrosynthesis

Answer 3

Disconnect C-O with water then disconnect amide with HCl

Question 4

Imidazole retrosynthesis

Answer 4

Taut, disconnect 2xC-N bonds then hydrolyse 2xC=N bonds

Question 5

Thiazole retrosynthesis

Answer 5

Disconnect C-N bond (more reactive) then disconnect C-S using HCl

Question 6

Isoxazole retrosynthesis

Answer 6

Disconnect C-O then hydrolyse C=N

Question 7

Pyrazole retrosynthesis

Answer 7

Disconnect C-N then hydrolyse C=N

Question 8

Isothiazole retrosynthesis

Answer 8

Disconnect N-S bond then hydrolyse C=N

Question 9

EAS of 1,2-Azoles

Answer 9

Less reactive to E+ than Pyrrole so substitution at C4