L Le ev ve el l 2 2 – – C Ca as se e 1 18 8
U Un nu us su ua al l D Di ie el ls s- -A Al ld de er r R Re ea ac ct ti iv vi it ty y o of f
A Ac cy yc cl li ic c 2 2- -A Az za ad di ie en ne es s
K Ke ey y p po oi in nt t: : C Cy Cy Cy yc yc y yc yc yc yc y y l lo lo lo lo l loa ad dd dd d dd dd d dd d ddi di di d di di d dit ti ti ti t ti ti t tio io io io i ion ns s
N
CO 2 Me
Ph
CO 2 Et
EtO 2 C
N
CO 2 Me
Ph
N
N
CO 2 Me
Ph
EtO 2 C
EtO 2 C
NH
H
N
CO 2 Me
Ph
normal Diels-Alder
l
inverse Diels-Alder
U Un nu us su ua al l D Di ie el ls s- -A Al ld de er r R Re ea ac ct ti iv vi it ty y o of f A Ac cy yc cl li ic c 2 2- -A Az za ad di ie en ne es s
Azadiene 1, bearing an electron-withdrawing substituent (CO 2 Me), is expected to
be electron-deficient and, therefore, more likely to react with electron-rich dienot
philes in an inverse electron demand Diels-Alder reaction.
d
However, for a diene, 1
shows a very unusual reactivity, since it participates in cycloadditions with both
electron-rich and electron-deficient dienophiles. As an example, reaction of azadiene 1 with diethyl fumarate yields pyridine 2 whereas in the presence of N-cyclo- N N
penten-1-ylpyrrolidine, tetrahydropyridine 3 is obtained (Scheme 18.1).