B5 - Structure and Reactivity

how to determine stereochem of DA

layer diene and dienophile, place all Hs on the right, they are up

WH conditions for thermally allowed pericyclic reactions

(4q+2)s + (4r)a = odd

WH rules for photo allowed pericyclic reactions

(4q+2)s + (4r)a = even

for electrocyclic reactions with 4n e-, conrotary or disrotary for thermally allowed

con (now you can draw that table)

why do 4m rings open easily

release ring strain

what does conrotary mean

orbitals move in the same direction, either both clockwise or anticlockwise

what does disrotary mean

orbitals move opposite directions, one clockwise one anticlockwise

what product does a 2-diene produce

para product

what does product does a 1-diene produce

ortho product

what type of pericylic steps are there

• electrocyclic ring open/closing

• [n+m] cyclo additions

what to do if directing group on benzene doesn’t work with proposed mechanism

assume DG dominates then try a migration step (unfavourable 4* carbon for example)

requirements for benzyne

good LG and strong base (make sure it works w any directing groups too)

C=O with adjacent C=N2 mechanism

1. N- makes triple bond with N+

2. C=N donates to C-C bond

3. C=O becomes C-O-

4. C-O- to C=O

5. form carbene by kicking off N2 gas (entropically favourable)

how to look at stereochem for carbene stuff (probably)

draw chair or similar where possible

for TsN3, where would it be attacked (i.e. from deprotonated dicarbonyl)

terminal N

when there is a base, and an obvious H, what should you do

deprotonate

Amide + Br2/NaOH

1. forms nitrene

2. C-C migrates to C-N=C=O