7c Flashcards
when making pyrrole and pyridine,, what do we need to do
we need to look at our product and at our starting materials.
we need to label the carbons that make up the ring,, not the substituents
we then need to see how to join the 2 compounds together: aka what bonds need to form and between what
we then need to identiy what is the nuc and what are the electrophile.
we then do the reaction mechanism based on all this.
when we have a arbon and a carbonyl that need to bond,, what will be the nucleophile and what will be the electrophile
the carbonyl will be the electrophile.
meaning the random carbon needs to be the nucleophile.
to make it a nucleophile u need to see if there are any ewg next to it bc ur gonna have to form an enol // enolate to attack the carbonyl.
how do we form an enolate
by deprotonating a carbon and forming a double bond connected to a carbonyl,, which makes O-.
ketones can be transformed to what
they can be transformed to enolssss
aka from a carbonyl u get a double bond with an OH connected to it.
to form it think of a deprotonation reaction where u then protonate the O- to form an enol.
how can we make a carbon nucleophilic
we make an enol,, so the C is part of the double bond that attacks an electrophile to form a bond and connect those 2 things together
normally we have to oxidise the reaction in order for what
we oxidise the reaction in order to regain aromaticity.
loss of H’s!!! to form double bonds and make the pyrrole // pyridine aromatic againnnnn
when do we not have to oxidise the reaction to form our pyrrole // pyridine product
we dont need to oxidise it if the startig material has a double bond in the correct place!!! bc obvs theres no H’s there anymore.
aka in alpha beta unsaturated 1-5 dicarbonyls.
aka a carbonyl with a double bond near it.
okay so once we form the ring but we still have the OH what do we need to do
use the N: to kick them off,, then remove H’s to form double bonds and neutralise the N.
how can double bonds be formed
- oxidation MnO2, O2, H2O2
- elimination reaction!! the waterfall thing,, aka remove a H and use the e- to form a doubel bond!!
use NH2OH for elimination reactions!!
to form the last double bonds to regain aromaticity,, what do we need to do
we need to either oxidise it
or do an elimination reaction to form a double bond.
when we have a carbonyl with a CtripleC alpha to it,, what are the 2 diff places we can make electrophilic
the C of the carbonyl
and the 2nd C away from the carbonyl C.
this can be done and seen when we resonate the carbonyl double bond onto the O.
or when we resonate the Ctriple C bond onto the oxygen!!!
basically we just resonate everything onto the O and see where we get a (+)
sometimes we need to think abput diff forms,, like
enols and ketones
also immines and amines!!1 by moving double bonds to form C=C instead of immines etc.
is a C bonded to a halogen electrophilic or nucleophilic
its electrophilic
meaning it will be attacked by a nucleophile
whats a furan
a pyrrole with an ‘O’ instead of an N.
whats a thiophene
a pyrrole with an ‘S’ instead of an ‘N’.
how do we make furans
furans:
di carbonyl + H+
one of the carbonyls becomes an enol and the other is a protonated carbonyl.
the enol attacks the carbonyl C and kicks off the carbonyl? to make a furan
remove any other groups by elimination to get a furan
how do we make a thiophene
di carbonyl + a S source.
u make one of the carbonyls a CS single bonded and the other a CS double bonded
the single bonded will attack the carbon of the double bonded and kick it off giving u a thiophene.
name a S source for making thiophenes
NaS
LAWESSONS REAGENT.
what is the role of a lawessons reagent
makes a C=O into a C=S
its a source of sulphur.
whats an indole again
an indole is a benzene and a pyrrole fused together via a bond.. as in they share a bond!!!
whats the one way we learnt how an indole is made
we learnt the fischer indol reaction!!
what two things do we need to clock to know a fischer indole reaction is occuring
we need an aromatic hydrazine: aka an aromatic molecule with NH and NH2 attached to it. the NH and NH2 need to be in a chain.
we also need a ketone // carbonyl with alpha hydrogens ,, ones thaat can be removed for an enolate to form!! it needs to be able to undergo tautomerisation
in a fischer indole synthesis u have the aromatic hydrozine and u also have the enolisable ketone with obvs,,,, 2 R groups next to it,, when we form the indole,, what parts of the starting material will the product contain
the indole: aromatic and pyrrole fused together will haveeee the R groups from the enolisble ketone on it!!
and even tho the aromatic hydrazine has 2 N’s,, the indole will only have 1 N,, the pyrrole N.
how does the fischer indole reaction occur
the NH2 attacks the enolisable ketone and forms a bond,, u then want to kick off water using N:
u then do taut,, and instead of C=N u get C=C!!
u then need it to be in a 3,3 sigmatropic arrangement (a 6 membered transition state) where each fragment contributes 3 atoms
e- and bonds are then moved around and NN bond is cleaved, a double bond also becomes a single bond.
then bc u have C=N,, the C will be electrophilic so the N: can attack this C and kick off the NH.
why is the 3,3 sigmatropic arrangement favoured
bc ur going from NN sigma to CC sigma + regaining the aromaticity u lost
this is the driving force of the rearrangement.
what conditions favour // need to occur for the fischer indole reaction to occur
u need high temp!! or acidic conditionsssss
are heteroatoms normally ur electrophile or nucleophile
theyre normally ur nucleophilic sites!! aka they have lone pairs that can attack other parts of molecules to form bonds
whats a 1H- imidazole
a pyrrole but with an extra N at the top of the 5 membered ring.
so u have a 5 membered ring where 2 of the things are N. there are 2 double bonds
the N and N have a C between them. N C N
whats an oxazole
an oxazole is a 5 membered ring with O and N.
N C O
N is at the top and O is where the pyrrole N normally is.
there are also 2 double bonds in the structure.
whats a thiazole
a thiazole is a 5 membered ring with S and N.
N is at the top,, then u have a C,, and then u have an S where the N of pyrrole normally is.
so u have N C .
2 double bonds aswell.
whats tha azole functional group,, shouldve asked this before
azole = 5 membered ring where u have N at the top and X at the bottom right.
X can be N, O, S.
there are 2 double bonds in it.
what are the diff ways u can make azoles
u can cut and form bonds between different positions.
