Dizincation of a 2‐Substituted Thiophene: Constructing a Cage with a [16]Crown‐4 Zincocyclic Core

Abstract

Metal detector: a bowl-shaped nanomolecule (see picture; S yellow, C gray, Zn blue) containing an unprecedented 16-atom [ZnC(3)](4) "anti-crown" ring has been unearthed by isolating a dizincated 2-substituted thiophene intermediate that would normally be hidden in tandem functionalization methodology.

Adding a Structural Context to the Deprotometalation and Trans‐Metal Trapping Chemistry of Phenyl‐Substituted Benzotriazole

“…For example,o ur own earlier work probing the alkali-metal-mediated zincation of N,N-diethyl-thiophene-2-carboxamide by the sodium zincate reagent [(TMEDA)Na(TMP)(tBu)Zn(tBu)] [22] produced an ice example of a1 6-membered (ZnCCC) 4 ring. [23] This smaller zincocyclei sr elated to that in 5,b ecause the ring arises from double deprotonation of the thiophene unit (compare that of the benzotriazole unit in 5), but in contrast, it was produced by direct zincation (Zn/H exchange) unlike the indirect lithiation/zinc-trapping mechanism at work in the synthesis of 5 (or the lithiation/aluminiumt rapping in 3 and 4; Scheme 4).…”

An alternative picture of alkali-metal-mediated metallation: cleave and capture chemistry

“…Whereas a redox mechanism is implicated in the formation of 1 : 1 ICEs, the participation of THF suggests that a metallation mechanism is more likely in the case of super ICEs. The loss of two Brønsted basic components from the original mixed metal mixture could be indicative of a twofold metallation of THF (there is precedence for a mixed metal multicomponent reagent acting as a di-base to effect a twofold metallation of the same substrate 28 ), but given the low super ICE yields obtained (less than 20%) it is conceivable that several competitive processes are in operation leading to other as yet unidentified products.…”

Heterobimetallic metallation studies of N,N-dimethylphenylethylamine (DMPEA): benzylic C–H bond cleavage/dimethylamino capture or intact DMPEA complex

“…Reagent 1 is a structurally well-defined crystalline compound [25] and efficient metallating (zincating) agent [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] [most recently with Nheterocyclic carbenes (NHCs) [42] ] though it has occasionally also been utilized as a nucleophilic t-butyl source. [43][44] Reagent 2 is a putative compound in that it has only been generated in situ by mixing LiTMP, Bu [45][46][47][48][49] which has been extensively studied.…”

“…AMMM reactions with DMPEA and characterization of "captured products" Due to the success of zincate (and aluminatesee below) systems in capturing and stabilizing the cyclic α-C 4 H 7 anion of THF, we opened the study by reacting DMPEA with the sodium monoamido-bisalkylzincate [(TMEDA)Na(TMP)(Bu t )Zn(Bu t )] 1 and the related lithium zincate [(PMDETA)Li(TMP)Zn(Bu t ) 2 ] 2 (TMEDA is N,N,N′,N′-tetramethylethylenediamine; TMP is 2,2,6,6,-tetramethylpiperidide; PMDETA is N,N,N′,N″,N″-pentamethyldiethylenetriamine) (Scheme 2). Reagent 1 is a structurally well-defined crystalline compound 25 and efficient metallating (zincating) agent [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] [most recently with N-heterocyclic carbenes (NHCs) 42 ] though it has occasionally also been utilized as a nucleophilic t-butyl source. 43,44 Reagent 2 is a putative compound in that it has only been generated in situ by mixing LiTMP, Bu t 2 Zn, and PMDETA in a 1 : 1 : 1 ratio in hexane solution, though it is a close relation of the Kondo/ Uchiyama THF-solvated reagent [(THF)Li(TMP)Zn(Bu t ) 2 ], [45][46][47][48][49] which has been extensively studied.…”