Cycloadditions of 2-Azaallyllithium Species with Conjugated Polyenes

Abstract

2-Azaallyllithium species [R(1)CH(-)N=C(X)R(2)Li(+), where R(1) and R(2) are alkyl and X = OMe] were generated by tin-lithium exchange of (2-azaallyl)stannanes and underwent [pi4s+pi2s] and [pi6s+pi4s] cycloadditions with cyclic dienes and trienes, respectively, to generate novel bridged azabicyclic compounds in a highly diastereoselective endo fashion. The periselectivity using cycloheptatriene was modest, producing a 1:1 mixture of [pi6s+pi4s] and [pi4s+pi2s] adducts. The reactions of 2-azaallyllithium species with dienes proceeded by a [pi4s+pi2s] pathway. The cycloadducts derived from cyclic 2-azaallyllithium species possess the 7-azabicyclo[2.2.1]heptane (tropane) or 8-azabicyclo[3.2.1]octane ring system and have been elaborated into cocaine-like analogues.

Unsaturated Derivatives of Trifluoromethanesulfonamide

“…Although the next member of the cyclic polyenes – cyclohepta‐1,3,5‐triene – is capable of acting as a diene, in the oxidative system used ( t BuOCl + NaI) it does not react with triflamide but rather is oxidized to benzaldehyde . Apparently the aromatization due to the ring contraction makes the oxidation of cyclohepta‐1,3,5‐triene easier than oxidation of triflamide to N ‐iodotriflamide.…”

Perspectives on Intermolecular Azomethine Ylide [3+2] Cycloadditions with Non-Electrophilic Olefins

“…34 This reactivity was further extended to other cyclic diene substrates, using both deprotonation and tin transmetallation as the source of 2-azaallyl anion intermediates. 35 Scheme 4 Reactivity of 2-aza-allyl anions with dienes and polyenes.…”

“…On dienes, only a densely-functionalized specimen was found to react with the 2-aza-allyl anion through a [4+3] cycloaddition (Scheme 4, b). 35 The reactivity of cycloheptatriene in this chemistry is rather capricious leading to [6+3] cycloadducts in some instances. [35][36] The formation of [3+2] and carbolithiation co-products is suggestive of a competitive step-wise mechanism operating when using these conjugated systems.…”

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

“…The most significant contributions to the generation and use of nonstabilized 2-azaallyl anions were made by Pearson and co-workers (see section ). − At the other end of the spectrum are the stabilized 2-azaallyl anions, wherein the negative charge is predominantly associated with an appropriate electron-withdrawing substituent, e.g., carbonyl, nitro, nitrile, phosphate, etc. In contrast to their nonstabilized counterparts, these anionic species are typically stable under aqueous conditions.…”