Ladderane

In chemistry, a ladderane is an organic molecule containing two or more fused cyclobutane rings. The name arises from the resemblance of a series of fused cyclobutane rings to a ladder. Numerous synthetic approaches have been developed for the synthesis of ladderane compounds of various lengths. The mechanisms often involve , a useful reaction for creating strained 4-membered rings. Naturally occurring ladderanes have been identified as major components of the anammoxosome membrane of the anammox bacteria, Planctomycetes.

Synthetic approaches have yielded ladderanes of varying lengths. A classification system has been developed to describe newly synthesized ladderanes, which is shown at right. The length of the ladderane is described by the number in brackets that precedes the word "ladderane". This is equal to the number of bonds shared by two cyclobutanes (n) plus 1. If the chain becomes long enough, it can cyclize onto itself, forming the band structure of the prismanes and related compounds.

Ladderanes have two types of stereochemical relationships. One describes the relative arrangement of hydrogen atoms at the fusion between two cyclobutane rings. These hydrogen atoms can be in either the cis- or trans- configuration. Trans-ladderanes have not been synthesized due to the ring strain in these compounds.

The second stereochemical relationship describes the orientation of three consecutive cyclobutane rings, and therefore is only relevant to ladderanes of n ≥ 2. The two outer rings can be on the same face (syn) or on the opposite face (anti), of the center ring.

Various synthetic methods have been used for the laboratory synthesis of ladderane compounds. The three major approaches are (1) dimerization of polyene precursors, (2) the stepwise addition, one or two rings at a time, (3) and oligomerization. Several examples of ladderane synthesis are outlined below.

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