Effect of adjacent chiral tertiary and quaternary centers on the metal-catalyzed allylic substitution reaction

Preparation of Enantioenriched Alkylcarbastannatranes via Nucleophilic Inversion of Alkyl Mesylates for Use in Stereospecific Cross-Coupling Reactions

We report the preparation of enantioenriched secondary alkylcarbastannatranes via a stereoinvertive S_N2 reaction of enantioenriched alkyl mesylates and carbastannatranyl anion equivalents. Using this process, enantioenriched secondary alcohols may be converted into highly enantioenriched alkylcarbastannatranes, which are useful in stereospecific cross-coupling reactions.

Stereospecific Electrophilic Fluorination of Alkylcarbastannatrane Reagents

We report the use of isolable primary and secondary alkylcarbastannatrane nucleophiles in site-specific fluorination reactions. These reactions occur without the need for transition metal catalysis or in situ activation of the nucleophile. In the absence of the carbastannatrane backbone, alkyltin nucleophiles exhibit no activity towards fluorination. When enantioenriched alkylcarbastannatranes are employed, fluorination occurs predominately via a stereoinvertive mechanism to generate highly enantioenriched alkyl fluoride compounds. These conditions can also be extended to stereospecific chlorination, bromination, and iodination reactions.

Stereospecific Palladium-Catalyzed Acylation of Enantioenriched Alkylcarbastannatranes: A General Alternative to Asymmetric Enolate Reactions

We report the development of a Pd-catalyzed process for the cross coupling of unactivated primary, secondary, and tertiary alkylcarbastannatrane nucleophiles with acyl electrophiles. Reactions involving optically active alkylcarbastannatranes occur with exceptional stereofidelity and with net retention of absolute configuration. Because the stereochemistry of the resulting products is entirely reagent-controlled, this process may be viewed as a general, alternative approach to the preparation of products typically accessed via asymmetric enolate methodologies. Additionally, we report a new method for the preparation of optically active alkylcarbastannatranes, which should facilitate their future use in stereospecific reactions.

B(C6F5)3-Catalyzed transfer 1,4-hydrostannylation of α,β-unsaturated carbonyls using iPr-tricarbastannatrane

Tris(pentafluorophenyl)borane, B(C₆F₅)₃, has been found to be an effective catalyst to access the hydridoborate anion, [N(CH₂CH₂CH₂)₃Sn][HB(C₆F₅)₃], via hydride abstraction from the hypercoordinated tin reagent, iPr-tricarbastannatrane. This process has been applied to the B(C₆F₅)₃-catalyzed transfer 1,4-hydrostannylation of electron-deficient olefins, namely benzylidene barbituric acids. Insights into the mechanism have been obtained via a series of ¹H, ²H, ¹¹B, ¹³C, and ¹¹⁹Sn NMR spectroscopy, mass spectrometry, and labeling experiments.

Carbastannatranes: a powerful coupling mediators in Stille coupling

Carbastannatranes are better coupling mediators in Stille coupling due to easy transfer of axial Sn-bound hydrocarbyl substituent during transmetallation step.

Activator-free palladium-catalyzed silylation of aryl chlorides with silylsilatranes

The palladium-catalyzed silylation of aryl chlorides with silylsilatranes proceeds under activator-free conditions; hence, wide functional group compatibility is displayed and boryl and siloxy groups are able to survive. Experimental and computational studies revealed that smooth transmetalation from the silylsilatrane to the arylpalladium chloride is facilitated by strong interaction between the Lewis acidic silicon and the chloride.

Stereoretentive Pd-catalysed Stille cross-coupling reactions of secondary alkyl azastannatranes and aryl halides

The development of transition metal-catalysed cross-coupling reactions has greatly influenced the manner in which the synthesis of complex organic molecules is approached. A wide variety of methods are now available for the formation of C(sp(2))-C(sp(2)) bonds, and more recent work has focused on the use of C(sp(3)) electrophiles and nucleophiles. The use of secondary and tertiary alkyl nucleophiles in cross-coupling reactions remains a challenge because of the propensity of these alkyl groups to isomerize under the reaction conditions. Here, we report the development of a general Pd-catalysed process for the stereoretentive cross-coupling of secondary alkyl azastannatrane nucleophiles with aryl chlorides, bromides, iodides and triflates. Coupling partners with a wide range of electronic characteristics are well tolerated. The reaction occurs with minimal isomerization of the secondary alkyltin nucleophile, and with retention of absolute configuration. This process constitutes the first general method to use secondary alkyltin reagents in cross-coupling reactions.