Unexpected Decarboxylation‐Triggered o‐Hydroxyl‐Controlled Redox Condensation of Phenylglycines with 2‐Nitrophenols in Aqueous Media

Abstract

A decarboxylation‐triggered and o‐hydroxyl‐controlled hydrogen‐transfer strategy for the one‐pot synthesis of benzoxazoles from readily available amino acids and 2‐nitrophenols is reported. On the basis of this autoredox reaction, the C−N bond can be efficiently constructed to afford the desired products in moderate to good yields under transition‐metal‐free conditions in aqueous media.magnified image

Dehydrative Synthesis of Functionalized Skipped Dienes from Stabilized Phosphonium Ylides and Allylic Alcohols in Water

“…With our continuous interests in alcohol‐based alkylation and aqueous media reactions, herein, we wish to report a mild and activator‐free dehydrative cross‐couplings of stabilized phosphonium ylides with allylic alcohols in water media for the efficient synthesis of functionalized terminal skipped dienes (Scheme D). The method can also be applied to other common allylic alkylating reagents such as allylic ethers and esters under additive‐free conditions .…”

“…To our best knowledge, reports on the synthesis of functionalized terminal skipped dienes are still rare. [9] With our continuous interests in alcohol-based alkylation [10] and aqueous media reactions, [11] herein, we wish to report a mild and activator-free dehydrative cross-couplings of stabilized phosphonium ylides with allylic alcohols in water media for the efficient synthesis of functionalized terminal skipped dienes (Scheme 1D). [7] The groups of You and Tian have independently reported the allylic alkylation of phosphonium ylides with allylic esters or amines for the efficient synthesis of terminal functionalized skipped dienes (Scheme 1C).…”

“…The method can also be applied to other common allylic alkylating reagents such as allylic ethers and esters under additive-free conditions. Other protic solvents that were widely used as good hydrogen bond donors, [18] were also investigated, but the target 4 a were obtained only in low to moderate yields, showing that water is an indispensable solvent for the reaction (runs [7][8][9][10][11]. [13] Noteworthy, possibly owing to that water media is theoretically disadvantageous to dehydrative reactions, the activator-free dehydrative couplings of allylic alcohols in water are much rare.…”

“…[8] Possibly owing to the poor leaving character of the hydroxy group, allylic alcohols, more easily-available, cheaper and stable, have not been employed to streamline the synthesis of functionalized terminal skipped dienes. [9] With our continuous interests in alcohol-based alkylation [10] and aqueous media reactions, [11] herein, we wish to report a mild and activator-free dehydrative cross-couplings of stabilized phosphonium ylides with allylic alcohols in water media for the efficient synthesis of functionalized terminal skipped dienes (Scheme 1D). The method can also be applied to other common allylic alkylating reagents such as allylic ethers and esters under additive-free conditions.…”

“…The ligands were also investigated, but dppf is still the best one (runs 5-6). Other protic solvents that were widely used as good hydrogen bond donors, [18] were also investigated, but the target 4 a were obtained only in low to moderate yields, showing that water is an indispensable solvent for the reaction (runs [7][8][9][10][11]. Surprisingly, the reaction under air could also give the target 4 a in 80% isolated yield (run 12).…”