Tandem Inter [4 + 2]/Intra [3 + 2] Cycloadditions of Nitroalkenes. The Bridged Mode (β-Tether)^†

A new variation of the tandem inter [4 + 2]/intra [3 + 2] cycloaddition of nitroalkenes has been developed. This method involves the Lewis acid-promoted [4 + 2] cycloaddition of nitro olefins <b>12</b> with 1-alkoxy-1,4-dienes <b>3</b>. The resulting nitronates <b>13</b>, bearing a C(5) tethered dipolarophile, undergo thermal, intramolecular [3 + 2] cycloaddition to afford stable tricyclic nitroso acetals <b>14</b>, which can be subsequently reduced to unveil a new carbocycle <b>16</b>. Thus, in three steps, highly functionalized aminocyclopentanes can be stereoselectively constructed in high yield.