HIGHLY REGIOSELECTIVE ACCESS TO 7-SUBSTITUTED 1,4,7,10-TETRAAZACYCLODODECANE-1-CARBALDEHYDE DERIVATIVES - SYNTHETIC ASPECTS AND NMR ELUCIDATION OF THE STRUCTURES - X-RAY CRYSTAL-STRUCTURES OF 7-TRIPHENYLMETHYL-1,4,7,10-TETRAAZACYCLODODECANE-1-CARBALDEHYDE AND 7-TRIPHENYLMETHYLOCTAHYDRO-5H,9BH-2A,4A,7,9A-TETRAAZACYCLOOCTA[CD]PENTALENE

7-Substituted 1,4,7,10-tetraazacyclododecane-1-carbaldehydes have been prepared through the ring opening of orthoamide protected intermediates which, in turn, were obtained by reaction of mono N-substituted 1,4,7,10-tetraazacyclododecane derivatives with dimethylformamide diethyl acetal. Orthoamide ring opening occurs under mild reaction conditions and is highly regiospecific: A number of mono- and bi-dimensional NMR experiments have been performed to assign unambiguously the structure of the opened compounds. The regiochemistry of such compounds has also been confirmed by elucidation of the solid-state structure of 7-triphenylmethyl-l,4,7,10-tetraazacyclododecane-1-carbaldehyde by X-ray crystallography. The crystal structure of 7-triphenylmethyloctahydro-5H,9bH-2a,4a,7,9a-tetraazacycloocta[cd] pentalene has also been determined.