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Olefin metathesis promoted by a well-defined metal carbene complex has evolved into an efficient method for the construction of a broad range of carbocyclic and heterocyclic rings of varying size. The synthetic potential of the olefin metathesis has been further increased by combining various other C-C bond forming processes either in tandem or in sequence. Herein, application of Claisen rearrangement and olefin metathesis to prepare various intricate and/or biologically important targets has been described.

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The benzocyclobutene-based a-amino acid derivative, ethyl 5-acetamido-2,4,5,6-tetrahydro-1H-cyclobuta[f]indene-5-carboxylate is synthesized via coupling of a benzocyclobutene-derived dibromide with ethyl isocyanoacetate as the key step, followed by hydrolysis and subsequent acetylation. This methodology is generalized in order to prepare various linearly and angularly fused indane-based a-amino acid derivatives.Key words: a-amino acids, [2+2+2] cycloaddition, indane-based a-amino acid, benzocyclobutene, ethyl isocyanoacetate, diversityoriented approach Constrained a-amino acid derivatives play an important role in the design of peptide drugs and peptidomimetics. 1 In this respect, indane-based a-amino acid 2, which is regarded as a constrained analog of phenylalanine (1), is an important target (Figure 1). There are several drugs which possess an indane ring as the core structural unit, 2 and indane-related compounds have been used as ligands for asymmetric synthesis. 3 We have undertaken a program to design various indane derivatives using novel methods such as [2+2+2] cycloaddition, [4+2] cycloaddition, Suzuki-Miyaura cross-coupling and metathesis as key steps. 4-9 However, there is a need to assemble highly functionalized indane-based a-amino acid derivatives with intricate side chains. To expand the building-block approach toward indane ring systems, herein, we report the synthesis of linearly and angularly fused indane-based a-amino acid derivatives. Figure 1 Phenylalanine (1) and indane-based a-amino acid 2