Protected hydroxyl and carboxyl

Another very appealing Cr-assisted cycloaddition procedure, the [6-1-4] combination, affords bicyclo [4.4.1] undecane systems, that are otherwise difficult to make [27]. Thus, in the presence of (naphthalene)Cr(CO)3, cycloheptatriene 43 underwent clean cyclization with 2,4-trans,trans-hexadiene 49 to yield compound 50 in good yield (Scheme 14). Unlike the previously described [67H-2ti] cycloaddition, the catalytic [6-1-4] process requires Mg-powder to facilitate re-re-duction to the active Cr(0). The catalytic [6-1-4] cyclization has proven to be quite general and tolerates protected hydroxyl and carboxyl functionalities. 

Figure 7. Protected hydroxyl and carboxyl monomers and deprotectedpolymers...

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