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This paper describes an efficient and green access to functionalized and highly constrained heteropolycyclic derivatives via a microwave-accelerated cycloaddition and heterogeneous hydrogenation sequence.Over the past few years, a significant amount of research has been directed towards the development of new technologies for environmentally benign processes. 1 Recent developments in the field of green chemistry have been oriented toward adopting methods and processes that use less toxic chemicals, produce smaller amounts of by-products, and use less energy. 1 Microwave-accelerated reactions have attracted considerable attention in the past decade and many efficient eco-friendly syntheses of a variety of organic products were developed in water. [2][3][4] In pursuit of atom and energy economical reactions we wished to develop a sequential microwave-assisted cycloaddition reaction followed by a heterogeneous hydrogenation, 5 which is so far unprecedented, for an easy access to complex functionalized heteropolycyclic derivatives.We turned our attention to the efficient and green synthesis of sterically constrained prochiral didehydroamino acid derivatives of type 3, bearing both bicyclo[2.2.2]oct-7-enes and an unsaturated amino ketone or ester functionality. These substrates may be attractive precursors of sterically constrained heterocyclic derivatives, and to date there has been little work carried out in relation to their hydrogenation. 6 The synthesis of substrates 3 was based on the Diels-Alder reaction 7 of 2H-pyran-2-ones 1 8 with maleimides 2. Prompted by our previous results in microwave chemistry and in the transformations of pyran-2-one derivatives, 9 we decided to employ a green approach for the synthesis of 3. Our experiences in this field have shown that 2H-pyran-2-ones serve as useful dienes in reactions with alkenes (maleic anhydride, maleimides) 8c,9c and alkynes. 9d,e The cycloaddition of some fused pyran-2-ones with maleimides under drastic conditions (in boiling decalin or toluene) resulted in the synthesis of fused isoindoles accompanied in a few cases by double cycloadducts (fused bicyclo[2.2.2]octene derivatives); the latter were mainly detected, with one exception, as intermediates or side-products in the above reaction. 9c Therefore, we decided to develop an efficient and green methodology for the preparation of compounds 3 from 1 and 2, based on a microwave-accelerated reaction in an aqueous mixture (or under anhydrous conditions). Despite the low solubility of substrates 1 in water, cycloaddition was complete after microwave irradiation for 45 minutes at 150 °C (Table 1) affording the bicyclic derivatives 3 in excellent yields.In some cases, such as 3a (Table 1, entry 1) and 3f (entry 6), the use of water was not advantageous (complex mixtures of products including 3a or 3f were obtained), therefore, the reactions were carried out under anhydrous conditions, and the resulting adducts were crystallized from ethanol. The conventional synthesis of the same cycloadducts, such as 3b and 3e, re...