Formation of Cyclic Allenes and Cumulenes by Cooperative Addition of Frustrated Lewis Pairs to Conjugated Enynes and Diynes

Mömming, Cornelia M.; Kehr, Gerald; Wibbeling, Birgit; Fröhlich, Roland; Schirmer, Birgitta; Grimme, Stefan; Erker, Gerhard

doi:10.1002/anie.200906697

Cited by 137 publications

(87 citation statements)

References 89 publications

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“…Heterocyclic allenes have also been isolated as small as eight-membered rings, with a mixed 'P' and 'B' heteroatom ylid. 14 ring-expansion is relief of ring strain of the 7-membered allenic ring -therefore, there is a favourable energy balance between the 7-membered allenic ring formation, and its subsequent role in providing a driving force for ring expansion. An additional crucial component of this step is the presence of an electrophile (E) -the major product arising from the reaction, 7, requires E = H + , whereas the minor product 8 requires E = CO 2 , probably generated, on the basis of the results noted in Table 1, from carbonic acid decomposition, the acid in turn resulting ultimately from the Cs 2 CO 3 base via bicarbonate (see below for a greater discussion).…”

Section: Mechanistic and Reaction Discussionmentioning

confidence: 99%

Rapid Cascade Synthesis of Poly-Heterocyclic Architectures from Indigo

et al. 2013

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The base-induced propargylation of the dye indigo results in the rapid and unprecedented one-pot synthesis of highly functionalized representatives of the pyrazino[1,2-a:4,3-a′]diindole, pyrido[1,2-a:3,4-b′]diindole and benzo [b]indolo [1,2-h]naphthyridine heterocyclic systems, with the last two reflecting the core skeleton of the anticancer/antiplasmodial marine natural products fascaplysin and homofascaplysins and a ring Bhomologue, respectively. The polycyclic compounds 6-8, whose structures were confirmed through singlecrystal X-ray crystallographic analysis, arise from sequential inter/intramolecular substitution-addition reactions, and in some cases, ring rearrangement reactions. Preliminary studies on controlling the reaction path selectivity, and the potential reaction mechanisms, are also described. Initial biological activity studies with these new heterocyclic derivatives indicated promising in vitro antiplasmodial activity as well as good anticancer activity. The chemistry described is new for the indigo moiety and cascade reactions from this readily available and cheap starting material should be more broadly applicable in the synthesis of additional new heterocyclic systems difficult to access by other means. Preliminary studies on controlling the reaction path selectivity, and the potential reaction mechanisms, are also described. Initial biological activity studies with these new heterocyclic derivatives indicated promising in vitro anti-plasmodial activity as well as good anti-cancer activity. The chemistry described is new for the indigo moiety and cascade reactions from this readily available and cheap starting material should be applicable more broadly in the synthesis of additional new heterocyclic systems difficult to access by other means.

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Section: Mechanistic and Reaction Discussionmentioning

confidence: 99%

Rapid Cascade Synthesis of Poly-Heterocyclic Architectures from Indigo

et al. 2013

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“…It is known from previous publications that FLPs react with terminal alkynes via deprotonative borylation pathway, producing the respective onium alkynylborates 41,42,43,44,45,46 . Indeed, 6 reacts with hex-1-yne giving the respective adduct 31 (Scheme 6).…”

Section: Alkenes Under Hydrogenation Conditionsmentioning

confidence: 99%

A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes

et al. 2013

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Recently, a new approach to dihydrogen activation known as frustrated Lewis pairs (FLPs) concept has been introduced 1, 2, 3 . A combination of highly Lewis acidic boranes and sterically hindered bases can split hydrogen heterolytically generating onium (phosphonium, ammonium, etc.) borohydrides. These compounds show reduction activity resembling that of inorganic borohydrides like NaBH 4 , i. e. they are suitable mostly for reduction of polarized multiple bonds. Imines, enamines, silyl ethers 4, 5,6 , α,β-enones 7 , ynones 8 , Nalkylanilines 9 were hydrogenated using stoichiometric or catalytic amounts of FLPs. Due to heterolytic nature of FLP-H 2 adducts, hydrogenation of unactivated multiple C-C bonds using FLPs has some natural limitations, since during the respective step of the catalytic cycle a proton transfer from catalyst to substrate should take place (Fig. 1a). Although Greb et al. have implemented this approach to hydrogenation of alkenes under ambient conditions, this method is predictably restricted to the alkenes with high proton affinity 10 .

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“…However, the preorganization of Lewis acidic and basic sites that is achievable through the introduction of a linker can significantly aid in the fine‐tuning of FLP reactivity, and thus makes the additional synthetic effort worthwhile. For example, Erker and co‐workers studied a series of compounds R 2 P(CH 2 ) n B(C 6 F 5 ) 2 ( n =2–4) and found the ethylene‐ and butylene‐bridged species to be active FLPs (e.g., for H 2 cleavage), whereas the propylene derivative showed no indication of typical FLP activity …”

Section: Introductionmentioning

confidence: 99%

A Highly Reactive Geminal P/B Frustrated Lewis Pair: Expanding the Scope to C−X (X=Cl, Br) Bond Activation

Samigullin

Georg

Bolte

et al. 2016

Chemistry A European J

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The geminal frustrated Lewis pair tBu2PCH2B(Fxyl)2 (1; Fxyl=3,5‐(CF3)2C6H3) is accessible in 65 % yield from tBu2PCH2Li and (Fxyl)2BF. According to NMR spectroscopy and X‐ray crystallography, 1 is monomeric both in solution and in the solid state. The intramolecular P⋅⋅⋅B distance of 2.900(5) Å and the full planarity of the borane site exclude any significant P/B interaction. Compound 1 readily activates a broad variety of substrates including H2, EtMe2SiH, CO2/CS2, Ph2CO, and H3CCN. Terminal alkynes react with heterolysis of the C−H bond. Haloboranes give cyclic adducts with strong P−BX3 and weak R3B−X bonds. Unprecedented transformations leading to zwitterionic XP/BCX3 adducts occur on treatment of 1 with CCl4 or CBr4 in Et2O. In less polar solvents (C6H6, n‐pentane), XP/BCX3 adduct formation is accompanied by the generation of significant amounts of XP/BX adducts. FLP 1 catalyzes the hydrogenation of PhCH=NtBu and the hydrosilylation of Ph2CO with EtMe2SiH.

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Formation of Cyclic Allenes and Cumulenes by Cooperative Addition of Frustrated Lewis Pairs to Conjugated Enynes and Diynes

Cited by 137 publications

References 89 publications

Rapid Cascade Synthesis of Poly-Heterocyclic Architectures from Indigo

Rapid Cascade Synthesis of Poly-Heterocyclic Architectures from Indigo

A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes

A Highly Reactive Geminal P/B Frustrated Lewis Pair: Expanding the Scope to C−X (X=Cl, Br) Bond Activation

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