Abstract
Besides their biological activity, the importance of β-lactams as synthetic intermediates
has been widely recognized in organic synthesis because ring cleavage of any of the
four single bonds of the β-lactam system is enhanced by ring strain. Selective bond
cleavage of the 2-azetidinone ring coupled with further interesting synthetic transformations
renders these fascinating molecules powerful synthetic building blocks. Opening of
the β-lactam ring can occur through cleavage of any of the single bonds of the four-membered
ring. However, the sequential or simultaneous fragmentation of two bonds of the 2-azetidinone
ring has been seldom reported. The present account is a survey of the recent salient
synthetic achievements exploiting selective bond cleavage of the β-lactam nucleus,
with particular emphasis to diastereoselective processes. The usefulness of these
substrates for the preparation of substances of biological interest, including α-amino
acids, β-amino acids, indolizidines, pyrrolizidines, eight-membered lactams, and complex
natural products is presented. The majority of the reviewed work will be centered
in significant results from our research group. However, interesting results from
others workers will be included.
1 Introduction
2 Selective Bond Cleavage of the 2-Azetidinone Nucleus
2.1 N1-C2 Bond Breakage
2.2 C2-C3 Bond Breakage
2.3 C3-C4 Bond Breakage
2.4 C4-N1 Bond Breakage
3 Cleavage of Two Bonds of the 2-Azetidinone Ring
4 Summary
Key words
β-lactams - strain energy - selective bond cleavage - rearrangement reactions - stereocontrolled
synthesis
