Enantio- and Regioconvergent Synthesis of γ-Stereogenic Vinyl Germanes and Their Use as Masked Vinyl Halides

Abstract

A nickel-catalyzed enantio-and regioconvergent alkylation of regioisomeric mixtures of racemic germylated allylic electrophiles with alkyl nucleophiles is reported. Key to success is a newly developed hept-4-yl-substituted Pybox ligand that enables accessing various chiral γ-germyl α-alkyl allylic building blocks in excellent yields and enantioselectivities. The reason for the regioconvergence is the steering effect of the bulky germyl group. The resulting vinyl germanes can be easily halodegermylated without racemization of the allylic stereocenter to afford synthetically valuable γ-stereogenic vinyl halides.

Ni–H-Catalyzed Chemo- and Regioselective Hydroarylation of Vinylsilanes

“…Finally, having an heteroaryl unit such as a thienyl group attached to the silicon atom was also tolerated, enabling product formation in 55% yield (2f → 3af). In contrast to the reported hydroalkylation protocol for the anti-Markovnikov 5 and Markovnikov selectivity, 8 we did not observe any transformation with vinylgermanes (not shown).…”

“…This chemoselectivity is in accordance with that previously seen with the hydroalkylation protocol. 5 Notably, an allylsilane alone did not result in any product formation (not shown). Furthermore, a substrate decorated with an isopropenyl group in the presence of the vinyl moiety as in 2i confirmed once more the chemoselectivity of this protocol.…”

“…The starting point of this study was an examination of the hydroarylation reaction dimethyl(phenyl)(vinyl)silane (2a) with phenyl iodide (1a) by adapting the optimized conditions from the previously reported protocol for the hydroalkylation of vinylsilanes and -germanes (Table 1). 5 To our surprise, we were able to isolate the desired product 3aa with excellent regioselectivity when employing 2,2'-bipyridine (L1, bpy) as the ligand (entry 1). An evaluation of other bidentate nitrogen ligands such as dmbp (L2), BBBPY (L3), phen (L4 ), BPhen (L5) and quinox (L6) did not further improve the yield and regioselectivity (entry 2-6).…”

Cation-Assisted Hydrosilylation of Alkynes Catalyzed by a Low-Valent Iron Complex Bearing Noninnocent Ligands

“…Despite their lower toxicity and greater stability, organogermanes are valuable reagents that have been significantly less investigated than their tin-based analogs. − Hydrogermanylation of alkynes can be carried out with numerous noble-metal catalysts. Alternatively, non-noble-metal based systems achieving this transformation remain scarce .…”

Highly selective α-hydrogermylation of alkynes catalyzed by an in situ generated bulky NHC–cobalt complex

“…For instance, vinylgermanes can be easily converted into vinylhalides by halodegermylation in the presence of NBS or NIS, without changing the double bond geometry. 2,3 This, in combination with further derivatization of the halide-product, can serve as a very powerful method for the synthesis of complex molecules and natural products. [4][5][6] What is more, a significant improvement has been recently made in the field of C-C coupling using germanium derivatives.…”