A Diastereoselective Synthesis of 5–5 and 5–6 Fused Bicyclic Ureas via Cross‐Metathesis/Aza‐Michael Reaction Strategy

The synthesis of highly substituted, enantiopure 5–5 and 5–6 fused bicyclic ureas from sugar‐derived cyclic nitrones is described. The key precursors were prepared via Grignard addition, followed by NO bond cleavage and subsequent urea formation. Cross‐metathesis and aza‐Michael reactions served as the pivotal transformations, enabling access to the corresponding bicyclic ureas in good yields and with high diastereoselectivity. The 5–5 fused bicyclic ureas were obtained in moderate to good yields with diastereomeric ratios of up to 10:1, while the 5–6 fused analogues were isolated in good yields with diastereomeric ratios reaching 9:1.