Hydride alternate routes

The introduction of tritium into molecules is most commonly achieved by reductive methods, including catalytic reduction by tritium gas, PH2], of olefins, catalytic reductive replacement of halogen (Cl, Br, or I) by H2, and metal pH] hydride reduction of carbonyl compounds, eg, ketones (qv) and some esters, to tritium-labeled alcohols (5). The use of tritium-labeled building blocks, eg, pH] methyl iodide and pH]-acetic anhydride, is an alternative route to the preparation of high specific activity, tritium-labeled compounds. The use of these techniques for the synthesis of radiolabeled receptor ligands, ie, dmgs and dmg analogues, has been described ia detail ia the Hterature (6,7). 

An alternative route to a furanosyl halide of 2-deoxy-D-nbo-hexose was envisaged, involving the lithium aluminum hydride reduction of ethyl 2,3-anhydro-/ -D-allofuranoside which could, presumably, lead to ethyl... 

The potential participation of an alternative route, involving a binuclear elimination reaction between a metal-acyl and a metal-hydride has also been probed [73]. In Rh-catalysed cydohexene hydroformylation, both [Rh4(CO)i2] and [Rh(C(0)R)(C0)4] are observed by HP IR at steady state, the duster species being a potential source of [HRh(CO)4] by reaction with syn-gas. The kinetic data for aldehyde formation indicated no statistically significant contribution from binudear elimination, with hydrogenolysis of the acyl complex dominant. For a mixed Rh-Mn system. 

An alternative route to the polyoxybenzophenone involves cyclization of the triketo acid (512) to the pyranone (513) and subsequent rearrangement on treatment with lithium hydride (77JA1631). 

K2[H2W(CO)4]. The former were the first reported bis-phosphine-substituted derivatives of [M2(CO)i0]2 dianions, whereas [H2W(CO)4]2 is formally a diprotonated derivative of [W(CO)4]4 . High yields (70%) of [H2W(CO)4]2 were also obtained by the reaction of W(CO)4(TMED) with excess K[sec-Bu3BH] in THF. Treatment of [W2(CO)8L2]2- with water provided the hydride anions, [HW2(CO)8L2], which were isolated as Et4N+ salts and were characterized by elemental analyses and infrared and -NMR spectra. M. Darensbourg, and co-workers reported on alternative routes, not involving the dimetal dianions, [M2(CO)8L2]2, to similar substituted bridging hydrides of Mo and W (97,105,106). 

One conceivable pathway for the 1,6-enyne cyclization is a cyclo-pal ladation via complex 42 to cyclic palladium compound 43, which contains Pdlv, followed by cleavage of the latter to intermediate 44 that subsequently releases hydridopalIndium acetate and product 14-/. An alternative route proceeds by way of hydropalla-dation of the C-C triple bond to intermediate 45, which after addition to the C-C double bond gives bicyclic system 46. This leads to product L4-Z following a p-hydride elimination. The appearance of double-bond isomeric compound 15-Z is explained by another addition of the palladium species to the cyclic C-C double bond in 14-Z and subsequent p-hydride elimination. 

Alkyl chains are generally deposited on the silica surface using the corresponding alkylsilane. The hydride intermediate route, developed by Sandoval and Pesek78,79 gives an alternative for this method. The one-step alkylsilane route, is replaced by a two-step silanization-alkylation procedure. The loss of process simplicity is compensated by the advantages of an increased alkyl density and enhanced coating stability. 

An alternative route to the bromo or chloro derivative is derived from aluminum chloride-lithium aluminum hydride reduction of the corresponding 3-bromo- or 3-chloroacetylpyrrolo[2,3-6]pyridine (see Section 7.06.5.2.l(iii)) <82JHC665,84JHC421). 

Alternative routes to unimolecular reduction include hydrogen abstraction by ketyls (see (ii)), Meerwein-Ponndorf reduction by alkoxides [A]f and reduction by a reactive form of magnesium hydride... 

Variations in reaction conditions, particularly with respect to acid and iodide concentrations, have profound effects on the positions of these equilibria, and these have, for the most part, added significant complexity to the behavior of the systems. It has also been determined that the catalytic activity of the cobalt catalyst system is increased with the introduction of H2 (44) or halides (vide infra), though these increases in rate are quite often at the expense of selectivity. The presence of added H2 serves as an alternate route to the formation of the hydride species ... 

An alternative route that also gives good yields of 3-arylphthalazinium-l-olates (e.g., 205 Ar = Ph) has been described by Lund and involves thermolysis (100-120 C) of A-arylamino-3-hydroxyphthalimidines (197). This transformation (197 - 196) probably proceeds by formation of a hydrazide (198) prior to cyclodehydration (198 - 1%). Compound 205 (Ar = Ph) is obtained in low yields by lithium aluminum hydride reduction of 4-hydroxy-2-phenyl-l(2//)-phthalazinone 207 (R = OH, = Ph). ... 

Two alternative routes, which have been little exploited, are the thermal decomposition of an organotin formate, or the hydrolysis of a stannylmetallic compound, and a promising different approach involves the alkylation of a lithium tin hydride. 

The principal alternative route into the organotin(IV) manifold is based on the reaction of tin hydrides or stannylmetallic compounds, as shown in Scheme 1.1.2. The most common (radical) mechanism of hydrostannation of alkenes and alkynes with organotin hydrides is outlined, for alkenes, in Equations (1.1.5) and (1.1.6). 

On the other hand, the other process without involving the formation of r)3-allylic complexes may operate as an alternative route in the course of the C-O bond cleavage. One is the SN2 type attack of a ligand bound to the metal such as hydride, alkyl or alkoxide on the terminal carbon of the allylic entity. The process is followed by elimination of the OX group (acetate or alkoxide) in a concerted manner as shown in Eq. 4. The other mode of cleavage is insertion-elimination type as shown in Eq. 5. The process proceeds by insertion of the olefinic moiety of the allylic entity into the M-Y bond, such as hydride, alkyl, or alkoxide ligand followed by P-elimination of the acetate or alkoxide moiety. 

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