Synthesis of Heterocyclic Rings 1(Introduction & Substitution)

Ring SynthesisCyclization Reactions Cycloaddition Reactions Ring transformation

Nu

E

Ring enlargement

ring contraction

Baldwin's rules for ring closures

• Baldwin's rules in organic chemistry are a  series  of  guidelines  outlining  the relative  favourabilities  of  ring  closure reactions  in alicyclic compounds.  They were  first  proposed  by Jack Baldwin in 1976.

• The rules classify ring closures in three ways:• the number of atoms in the newly formed ring• into exo and endo ring closures, depending whether the bond broken during the ring closure is inside (endo) or outside (exo) the ring that is being formed

• into tet, trig and dig geometry of the atom being attacked, depending on whether this electrophilic carbon is tetrahedral (sp3 hybridised), trigonal (sp2 hybridised) or digonal (sp hybridised).

Cyclization Reactions• Displacement at saturated carbons

NH2

Br

NH2

Br

NH

NH

NH

NH2

Br

NH2

Br

NH

3-exo-tet 4-exo-tet 5-exo-tet 6-exo-tet

Examples

O OBr OO

-

The Darzens reaction (also known as the Darzens condensation or glycidic ester condensation) is the chemical reaction of a ketone or aldehyde with an α-haloester in the presence of base to form an α,β-epoxy ester, 

This reaction was discovered by the organic chemist Auguste George Darzens in 1904.[3]

N

R

XR

R

Br

Br

X

R

RNH

Br

X

RNH2

Feist-Benary Furane Synthesis

O

RR1

OH

Cl

CO2Et

R1O

Cl O

R

CO2Et

RR1

CO2Et

OO

RR1

OH

Cl

CO2Et

Pyridine

+

-

-

-Haloketone -Ketoester

N

OPh

N

OPh

Cl

(CH3)3CO- K+