Chiral calciumcatalysts for asymmetric hydroamination/cyclisation

Abstract

Calcium complexes supported by chiral 1,2-diamines have been shown to be efficient catalysts for the asymmetric hydroamination of amino-olefin substrates; the calcium complexes [Ca(NN(R)){N(SiMe(3))(2)}(THF)] (R = (t)Bu, (i)Pr, Ph, 4-C(6)H(4)F) give enantioselectivities of up to 26% which marks a significant increase based upon literature precedence. The structure of [Ca(NN(Ph)){N(SiMe(3))(2)}(py)] has been computed with density functional methods.

Enantioselective Main Group Catalysis: Modern Catalysts for Organic Transformations

“…Recent attempts to use the chiral calcium-BOX system observed in hydrosilylation reactions (see Scheme 12, section 4) have shown promise at inducing stereogenic centers in hydroamination reactions producing almost complete conversion, however, the scope of the reaction was limited to intramolecular cyclization as before, with poor enantioselectivities being reported (ca 10% ee). It can be hypothesized that similarly poor enantiomeric excess is seen for the same reasons as observed in hydrosilylation reactions [127][128][129]. As stated previously, one of the issues that sometimes opposes the widespread utilization of group 2 centered catalysts, in particular calcium, is their propensity for rapid ligand redistribution.…”

Calcium-43 chemical shift and electric field gradient tensor interplay: a sensitive probe of structure, polymorphism, and hydration

“…[1][2][3][4] Likewise, calcium occurs in a variety of minerals and glasses, and is present at a level of about 400 ppm in sea water. 5 Calciumcontaining materials find applications as high temperature superconductors, [6][7][8][9] in catalysis, [10][11][12][13][14][15] in hydrogen storage 16,17 and in solid-state proton conductors. 18 In light of this wide array of interesting applications, which in theory could be probed using calcium solid-state nuclear magnetic resonance (SSNMR) experiments, development of the spectroscopy of the only NMR-active nuclide of calcium (i.e., 43 Ca) remains somewhat lethargic [19][20][21] due to complications which arise when attempting to perform such experiments.…”

Divergent Elementoboration: 1,3‐Haloboration versus 1,1‐Carboboration of Propargyl Esters

“…The activation of carbon–carbon double and triple bonds by main group compounds has been a staple motif in the synthesis of a plethora of new element–carbon bonds such as C−C, C−H, C−N, C−B, and C−O bonds amongst many others . Seminal work by Wrackmeyer et al.…”

“…

This work showcasest he 1,3-haloboration reaction of alkynesi nw hich borona nd chlorine add to propargyl systems in ap roposed sequential oxazoliumborate formation with subsequent ring-opening and chloride migration.I na ddition, the functionalization of these propargyl esters with dimethyl groups in the propargylic position leads to stark differences in reactivity whereby a formal 1,1-carboboration prevails to give the 2,2-dichloro-3,4-dihydrodioxaborinine products as an intramolecular chelate.D ensityf unctional theory calculations are used to rationalize the distinctc arboborationa nd haloboration pathways. Significantly, this method represents am etalfree route to highly functionalized compoundsi nasingle step to give structurally complex products.The activation of carbon-carbondoublea nd triple bonds by main group compounds hasb een as taple motifi nt he synthesis of ap lethora of new element-carbon bonds such as CÀC, [1] CÀH, [2] CÀN, [3] CÀB, [4] and CÀO [5] bonds amongst many others. [6] Seminalw ork by Wrackmeyer et al showcasedap owerful methodology using trivalent boranes in conjunction with "activated" alkynes, that is, M-CC-R, where M = Si, Ge, Sn, Pb inter alia.

…”

“…The activation of carbon-carbondoublea nd triple bonds by main group compounds hasb een as taple motifi nt he synthesis of ap lethora of new element-carbon bonds such as CÀC, [1] CÀH, [2] CÀN, [3] CÀB, [4] and CÀO [5] bonds amongst many others. [6] Seminalw ork by Wrackmeyer et al showcasedap owerful methodology using trivalent boranes in conjunction with "activated" alkynes, that is, M-CC-R, where M = Si, Ge, Sn, Pb inter alia.…”