Seven-membered rings, ring-closing metathesis strategy

Abell and co-workers applied their ring-closing metathesis strategy for the synthesis of P-amino acids constrained by five- and six-membered rings to synthesize a seven-membered ring p-amino acid for incorporation into P-peptide mimetics. Treatment of diene 244 with a 5 mol % of 4 in benzene provided the corresponding P-amino acid derivative 245 in 96% yield. 

A number of seven-membered ring carbacyles have also been prepared using ring-closing metathesis as a key strategy. Many of these carbacycles are natural products or important synthons for the production of natural products. Several key examples are highlighted below. 

The ring-closing enyne metathesis has been used for the synthesis of alkenyl substituted six- and seven-membered cyclic enol ethers (Eq. 88) [144]. The reaction has been proposed as an element of the strategy for preparation of subunits of brevetoxins and ciguatoxins. 

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