Variations in ring size

The intramolecular reaction of diazo groups with ketones has also been examined in several systems. Early work studied the variation in ring size, substitution and chain length on the reaction outcome (Scheme 19). Despite the interesting synthetic potential for an intramolecular ring expansion reaction, relatively few examples have been reported (equations 25,2 26,22 and 2823). 

The complexes of ( 1) to (j ) can be demetallated and reduced (using sodium borohydride) to give, in economic yields, the free macrocycles (IR) to (12R) which constitute a matrix of ligand structural types (Fig. 1) systematic variation in ring size, the number type and disposition of donors has been achieved. 

Amino groups of functionally substituted phosphines easily undergo nucleophilic substitution. Mutual transitions were shown to exist for the aminomethyl derivatives of phenylphosphine (80IZV1438), acyclic compounds being transformed into cyclic ones with variation in the size of the rings [Eq. (45)]. 

A very interesting experimental observation of Jones et al. illustrates a different effect of strain on the efficiency of photochemical Bergman cyclizations.43d Variations in the size of the cycle which does not incorporate the whole enediyne system, but only the vinyl part of the enediyne moiety (in contrast to the previously discussed data) affect the yield of the cycloaromatized product. Initially, an increase in the ring size leads to an increase in yield (Scheme 16). 

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