Substrate-directed synthesis: The rapid assembly of novel macropolycyclic structures via stereoregular diels-alder oligomerizations.

An increasing appreciation of molecular architecture and design will provide a greater impetus to tackle the exciting and elaborate structural targets that will confront chemistry in the twenty-first Century. It is, therefore, of the upmost importance that methods by which outwardly complex chemical systems can be assembled selectively, rapidly, and efficiently, are devised. Towards this goal, a trebly diastereoselective tandem Diels-Alder reaction sequence has been developed. Subsequently, we have demonstrated how this synthetic methodology can be utilized for the synthesis of novel macropolycyclic molecular structures. In each cycloaddition, the stereoelectronic characteristics, that are inherent in part of the rigid bicyclic frameworks of both bisdienophile and bisdiene building blocks, are used to dictate their respective modes of reaction. The outcome of this substrate-directed approach to organic synthesis allows the rapid and highly-controlled assembly of an increasing range of apparently complex molecular structures. The diastereoselectivities that are witnessed in each cycloaddition are rationalized as involving kinetically-controlled transition-state effects. The rationalization is based upon maximal vicinal staggering and the subsequent minimization of torsional strain within the rigid bicyclic framework in the transition state. In this survey, the application of the repetitive Diels-Alder approach for the synthesis of a wide range of macropolycyclic molecular structures is examined. The potential of these compounds as ideal precursors in the preparation of intriguing hydrocarbons is revealed. The pivotal role played by the sequential use of mild and forcing conditions — most notably the use of thermally- and high pressure-promoted Diels-Alder reactions — to produce oligomeric compounds in a predictable and stepwise manner is documented. Throughout these discussions, special attention has been given to the methods employed for the purification and characterization of this new class of unnatural products. [ABSTRACT FROM AUTHOR]