Inter‐ and intramolecular hetero‐Diels‐Alder reactions, 37. Syntheses of the 3‐amino sugar glycosides rac‐4‐deoxydaunosaminide rac‐4‐deoxyristosaminide, and rac‐acosaminide
You can manage bookmarks using lists, please log in to your user account for this.
Media type:
E-Article
Title:
Inter‐ and intramolecular hetero‐Diels‐Alder reactions, 37. Syntheses of the 3‐amino sugar glycosides rac‐4‐deoxydaunosaminide rac‐4‐deoxyristosaminide, and rac‐acosaminide
Description:
<jats:title>Abstract</jats:title><jats:p>The hetero‐Diels‐Alder reaction of the phenylthio‐activated N‐monoacyl‐ and N,N‐diacyl‐enamino ketones <jats:bold>8a‐c</jats:bold> containing a methyl group at position 2 of the oxadiene with the electron‐rich dienophiles <jats:bold>9a‐c</jats:bold> yields the exo/endo adducts <jats:bold>10a‐d</jats:bold> and <jats:bold>11a‐d</jats:bold> in 82–95% yield with the endo adducts as the main products. The enamino ketone <jats:bold>8d</jats:bold> with a S‐ethyl group at C‐3 does not react. Hydrogenation of <jats:bold>11a</jats:bold> with Raney nickel in THF leads to the desulfurized dihydropyran <jats:bold>12</jats:bold>, whereas in MeOH gives stereoselectively the perhydrophthalimido derivative <jats:bold>13</jats:bold>, which, after deprotection, yields the β‐methyl glycoside <jats:bold>14</jats:bold> of rac‐4‐deoxydaunosamine. Under similar conditions <jats:bold>10c</jats:bold> is converted into the β‐ethyl glycoside <jats:bold>15</jats:bold> of rac‐N‐benzoyl‐4‐deoxyristosamine. Stereoselective hydroboration of <jats:bold>12</jats:bold> affords <jats:bold>17</jats:bold> and subsequent cleavage of the protecting group leads to the β‐methyl glycoside <jats:bold>18</jats:bold> of rac‐acosamine.</jats:p>