Alkene Reductions Employing Ethyl Acetate-Hydroxylahine, a Useful new Source of Diimide

Oxazoline N-Oxide-Mediated [2 + 3] Cycloadditions: Application to a Total Synthesis of the Hypocholesterolemic Agent 1233A

“…Unexpectingely, compound 23 proved to be unreactive under classical diimide reduction conditions. Finally, it turned out that when diimide was prepared from hydroxylamine hydrochloride, the dihydro compound 24 was isolated without reduction of the iodovinylic moiety. Classical acidic hydrolysis furnished the aldehyde 25 which was submitted in turn to a second Wittig olefination giving rise to the desired dipolarophile 26 .…”

Synthesis of 1-Benzyl-, 1-Alkoxyl-, and 1-Aminoisoquinolines via Rhodium(III)-Catalyzed Aryl C–H Activation and Alkyne Annulation

“…Interestingly, the use of hydroxylamine aqueous solution (50 wt %) could greatly improve the yield to 72% with the use of 1.0 equiv of KOAc (entry 7). The yield was continuously improved to 86% by increasing the dose of H 2 NOH to 3.3 equiv (entry 8), while further increasing the dose of H 2 NOH led to a drop in yield (entry 9), as 1a was partly reduced to diphenylethylenes by the excess H 2 NOH . Replacing the additive with CsOAc was nearly equally effective (entry 10), and the use of other bases such as NaOAc and K 2 CO 3 afforded inferior yields (entries 11 and 12).…”

“…The yield was continuously improved to 86% by increasing the dose of H 2 NOH to 3.3 equiv (entry 8), while further increasing the dose of H 2 NOH led to a drop in yield (entry 9), as 1a was partly reduced to diphenylethylenes by the excess H 2 NOH. 16 Replacing the additive with CsOAc was nearly equally effective (entry 10), and the use of other bases such as NaOAc and K 2 CO 3 afforded inferior yields (entries 11 and 12). Changing neither the dose of KOAc nor reaction temperature could improve the yields (entries 13−15).…”

Syntheses of Gymnothespirolignans B and C and Non-natural Isomer 9-Epi-gymnothespirolignan B

“…Several other reduction conditions were assessed without success. For example, diimide reduction 15 gave only 30% conversion and low diastereoselectivity (1:2 = 47:53), whereas one-pot hydroboration followed by protodeboronation 16 resulted in cleavage of the C9-O bond with no alkene hydrogenation.…”