On the Preparation and Determination of Configurational Stability of Chiral Thio- and Bromo[D₁]methyllithiums

Abstract

Thio- and bromo[D1]methyllithiums (ee 99%) were generated from the respective stannanes by tin–lithium exchange at temperatures ranging from 0 to −95 °C. Thio[D1]methyllithiums 6 were found to be microscopically configurationally labile on the time scale of the thiophosphate-α-mercaptophosphonate rearrangement even at −95 °C. Thio[D1]methyllithiums 13a and 13b underwent a thia-[2,3]-Wittig rearrangement down to −95 °C and 13b only down to −50 °C. The former were microscopically configurationally stable below −95 °C, and the latter racemized completely at −50 °C. Chiral bromo[D1]methyllithiums are chemically unstable at −78 °C but microscopically configurationally stable at the time scale of their addition to benzaldehyde and acetophenone.

On the Configurational Stability of Chiral Heteroatom‐Substituted [D1]Methylpalladium Complexes as Intermediates of Stille and Suzuki–Miyaura Cross‐Coupling Reactions

“…The sodium salt of benzylmercaptane ( 8 ) was alkylated with mesylate[8b] 9 to yield sulfide 10 [9]. The thioacetate 11 was obtained in 84 % yield by the Mitsunobu reaction[19] of stannylmethanol 3 with thioacetic acid.…”

“…We concentrated on these most simple cases, the chiral α-heteroatom-substituted methyllithium compounds[7] 1 , and studied their microscopic (on the time scale of a rearrangement) and macroscopic (addition to benzaldehyde after aging) configurational stability (Figure 1). The substituent X comprised oxygen-,[8] sulfur-,[9] and nitrogen-containing[10] moieties and chloride[11] and bromide [9]. In summary, chiral methyllithium compounds with oxygen as heteroatom were configurationally stable at –78 °C or even higher temperatures, whereas nitrogen-containing chiral methyllithium compounds were only partly stable even at –95 °C.…”

Formation of Olefins by Eliminative Dimerization and Eliminative Cross‐Coupling of Carbenoids: A Stereochemical Exercise

“…Fortunately,t he data reveal that most, if indeed not all, carbenoids of interest are configurationally stable beyond the time scale necessary for the formation of the ate complex, ac ritical determinant of whether or not stereochemical information carefully placed within precursors can usefully impact the configuration of aproduct alkene.Even the most sensitive of carbenoids listed in Table 1, a-chloroalkyllithium compounds (entries 4and 5), have some degree of macroscopic configurational stability, but in this case they must typically be trapped in situ as soon as formed because of their extreme chemical instability. [8,9] This overall encouraging picture should nonetheless be restricted in the case of halogen-containing carbenoids. Ty pical for carbenoids,t hey are subject to nucleophilic substitution.…”

“…For this purpose the tin–lithium exchange reaction has proven to be reliable (e.g. entries 2 to 4) . However, relying on tin–lithium exchange reactions to generate stereochemically defined carbenoids only shifts the problem to the task of creating stereodefined α‐substituted organotin compounds.…”

Olefin‐Bildung durch eliminierende Dimerisierung und eliminierende Kreuzkupplung von Carbenoiden: eine stereochemische Herausforderung

“…Glücklicherweise erweist sich die Zinn‐Lithium‐Austauschreaktion als zuverlässig (Nr. 2–4) . Allerdings verschiebt man mit dem Rückgriff auf die Zinn‐Lithium‐Austauschreaktion zur Erzeugung stereodefinierter Carbenoide nur das Problem auf die Aufgabe, stereodefinierte α‐substituierte Organozinnverbindungen zu erlangen.…”