Reagents for Storage and Regeneration of Nonstabilized Azomethine Ylides: Spiroanthraceneoxazolidines

Abstract

Nonstabilized azomethine ylides are easily trapped by anthraquinone to form stable spiro-oxazolidines, which have an unusual ability to undergo a cycloreversion in the presence of other dipolarophiles at 120-150 °C. All tested recycloadditions with carbonyl compounds and electron-poor alkenes occurred in moderate to high yields (41-92%). Moreover, increasing the reaction temperature to 210 °C made it possible to obtain adducts with low reactive dipolarophiles.

Nitro-Substituted Benzaldehydes in the Generation of Azomethine Ylides and Retro-1,3-Dipolar Cycloadditions

“…In contrast to the parent Diels–Alder cycloadducts, which have the tendency to undergo retro-[4 + 2]-cycloaddition reactions, pyrrolidines are considered to be very stable [3 + 2]-cycloadducts . However, preformed unstable and stable oxazolidine cycloadducts were observed to undergo retro-1,3-DCA (cycloreversion) and the generated stabilized/nonstabilized azomethine ylides were trapped by dipolarophiles . Pyrrolidinofullerenes endured retro-cycloaddition reactions under microwave, thermal, and catalytic conditions to regenerate the parent fullerenes .…”

2-Azaallyl Anions, 2-Azaallyl Cations, 2-Azaallyl Radicals, and Azomethine Ylides

“…As outlined in Scheme , there are several different synthetic strategies for the generation of N-protonated azomethine ylides ( 289 ) and their N-alkylated cousins ( 290 ) including (1) ring-opening reactions, (2) deprotonation, (3) 1,2-prototropic rearrangement, (4) decarboxylation, (5) disilylation/destannylation, and (6) via carbenes and carbenoids. The most classical method involves the thermal (or photochemical) retro -pericyclic ring opening of aziridines ( 291 ). − The mechanism of this ring-opening process and the ensuing 1,3-dipolar cycloaddtions have been investigated thoroughly. − More recent innovations include the use of Lewis acids to mediate the ring-opening of aziridines to azomethine ylides at lower temperatures. − Dihydrooxazoles ( 292 , X = O), ,− dihydrothiazoles ( 292 , X = S), and related heterocycles ,, also can produce N -alkyl azomethine ylide dipoles via ring-opening processes.…”

Highly Efficient and Diastereoselective Construction of Substituted Pyrrolidines Bearing A Quaternary Carbon Center via 1,3-Dipolar [3 + 2] Cycloaddition

“…well-established methods for the chemo-and stereoselective construction of polyfunctional pyrrolidines in a single step [10][11][12][13][14]. In particular, azomethine ylides of non-stabilized type generated in situ from N-(methoxymethyl)-N-(trimethylsilylmethyl)-alkyl-amine are highly reactive intermediates [15], which reached with a diverse range of dipolarophiles to afford various nitrogen compounds via [3 + 2] [16-24] or [3 + 3] [25,26] cycloaddition reactions. Moreover, the non-stabilized azomethine ylides could take place the C≡N bond of some containing cyano-group compounds (Scheme 1a) [27].…”