Sodium hydride dimer

Another factor to consider is the energy required to break solid MH into individual molecules. Calculate the dissociation energies for sodium hydride dimer and potassium hydride dimer, i.e. 

Reinhoudt, Gray, Smit and Veenstra prepared a number of monomer and dimer crowns based on a variety of substituted xylylene units. They first conducted the reaction of 1,2-dibromomethylbenzene and a polyethylene glycol with sodium hydride or potassium Z-butoxide in toluene solution. Mixtures of the 1 1 and 2 2 (monomer and dimer) products were isolated and some polymer was formed . The reaction was conducted at temperatures from 30—60° and appeared to be complete in a maximum of one hour. The authors noted that the highest yield of 1 1 cyclic product was obtained with disodium tetraethylene glycolate instead of dipotassium hexaethylene gly-colate (see also Chap. 2) . Chloromethylation of 1,3-benzodioxole followed by reaction with disodium tetraethylene glycolate afforded the macrocycle (29% yield) illustrated in Eq. (3.20). 

Reaction of the cyclometallated complexes 244-246 with pyrazole and excess sodium hydride affords cyclic dimers 247 (990M3991), where C N denotes the corresponding cyclometallated ligand in accordance with structures 244-246. The [Pt2(thienylpyridine)2(/j.-pz)](C104)3] is known as well. 

The resting state of the propanoate catalysts may well be an acyl complex [60,61], while the attack of alcohol at the acylpalladium complex is considered to be the rate-determining step. It is probably more precise to say that fast preequilibria exist between the acyl complex and other complexes en route to it and that the highest barrier is formed by the reaction of alcohol and acylpalladium complex. The precise course of the reaction is still not known presumably deprotonation of the coordinating alcohol and the migratory elimination are concerted processes, accelerated by the steric bulk of the bidentate ligand. Toth and Elsevier showed that the reaction of an acetylpalladium complex and sodium methoxide is very fast and occurs already at low temperature to give methyl acetate and a palladium(I) hydride dimer [46]. 

The elimination of the sodium hydride was explained by the process given by Margeri-son and Nyss 289). Following Schmitt 296), Comyn and Glasse also proposed 309) that reaction of the anions formed in the a-methylstyrene system would yield deactivated species via reaction with the solvent, THF. Their kinetic study showed 310) that the process given in Eq. (68) was second order in monomer and first order in active centers, which are not consumed in the reaction. The sequence shown as Eq. (69) was found to be first order in active center concentration and in the dimer which is the product of Eq. (68). 

Treatment of 2-thiouracil with diiodo- or dibromomethane in the presence of sodium hydride in DMF gave the dimeric heterocycle 195 as a main product together with small amounts of the 1,3-thiazetidine derivative 196 and the trimeric heterocycle 197 (Equation 20 Table 15) <1996CL1099>. 

Oxazolidinones are the products of the acid-catalyzed condensation of a-hydroxyamides with aldehydes and ketones (equation 178). Tertiary amides derived from pyruvic acid undergo intramolecular cyclization when irradiated (equation 179) (78JOC419). Treatment of the a-bromo amide (308) with sodium hydride yields inter alia the dimeric oxazolidinone (309), presumably by way of an a-lactam, which adds to the carbonyl group of a second molecule of the amide (equation 180) (80JCS(P1)2249). 

The illustrated product results from a dimerization of the starting material through a multistep process. As illustrated below, initial deprotonation of the starting material with sodium hydride generates an acyl anion that adds, through a 1,4-addition, to the carbonyl of a second starting material molecule. Subsequent proton transfer sets up the intermediate species for an aldol condensation. 

Laurone has been prepared by hydrating and decarboxylating decylketene dimer.3 It has also been prepared by distilling calcium laurate 4 by heating lauric acid with phosphorus pent-oxide 5 by heating barium laurate under reduced pressure 6 by the ester condensation of ethyl laurate with sodium ethoxide 7 or of methyl laurate with sodium hydride 8 followed by ketonic hydrolysis by catalytic ketonization of lauric acid over a chromate catalyst 9 or by passing lauric acid over thorium dioxide at 400°.10... 

Reaction of 2,2 -(benzylazanediyl)diethanol with methylene chloride in THF in the presence of sodium hydride leads to 24% yield of 6-benzyl-l,3,6-dioxazocane 69 (Scheme 14, Section 14.08.6.1 <2001 H(54) 151 >), accompanied with 35% of dimeric 6,14-dibenzyl-l,3,9,ll-tetraoxa-6,14-diazacyclohexadecane (not shown in the scheme). 

LACTAMS Catecholboranc. Dimethyl-ketene. Hexamethyldisila2ane. Hydroxyl-aminc-O-sulfonic acid. o-Nitrophenyl thiocyanate. Palladium(II) acetate. Rhodiuin(H) acetate dimer. Sodium hydride. 

Reaction of 13 [R2 = C(4-CH,OC6H4)(C6H5)2] with guanidine hydrochloride in the presence of sodium hydride in dry dimethylformamide at 20 CC gives l-[2,3-dideoxy-2,3-(2-iminoimidazo-lidino)-5-0-[(4-methoxyphenyl)diphenyImethyl]-/ -D-ribofuranosyl]uracil 18 in 54% yield, while 13 (R2 = H) under similar conditions gives the dimeric iV1,W3-a-fused-(2-iminoimidazo-lidine)uridine 19 in 35% yield106. 

In the laboratory of T.R. Hoye, a HWE macmcyclic head-to-tail dimerization was used to construct the C2-symmetric macrocyclic core of (-)-cylindrocyclophane A. The monomer phosphono ester aldehyde was subjected to sodium hydride in benzene containing a catalytic amount of 15-crown-5 ether and 55% of the ( , )-macrocyclized product was obtained. None of the (Z,Z) stereoisomer was observed. Macrocyclization reactions usually require high-dilution conditions but even relatively concentrated solutions (0.02M) did not decrease the yield of the product in this case. 

Our first synthesis of a simplified southern portion was based on work done by Buchi (8) (Scheme 3). Protection of the dimer of acrolein 20 as a SchifTs base with t-butyl amine, followed by proton abstraction with a Grignard reagent and methyl ati on and deprotection gave 21. Reaction with trimethylphosphonoacetate (TMP) in the presence of sodium hydride gave the a, B unsaturated ester 22, which at 200 underwent a Claisen rearrangement to give the aldehyde ester 23 as a mixture of trans and cis isomers. The cis isomer in the presence of base epimerized mainly to the trans form. 

The dimer 147 and the carbinolamine 140b reacted with alcohols in the presence of an acidic catalyst to give the corresponding alkoxymethyl derivatives, e.g., 140a. Nitrosation of the N—H group, to give the N-nitroso compound 18b, readily occurred when the dihydrothiazine 18a was treated with sodium nitrite and hydrochloric acid in aqueous dioxane. There is only one report of the A -alkylation of a dihydrothiazinone this involves the A/ -methylation of the derivative 80a in the presence of methyl iodide and sodium hydride. ... 

Open-chain compounds also react to give these types of macrocycles. For example, 2-(hydroxymethyl)-6-(bromomethyl)pyridine reacted in the presence of sodium hydride to give the dimer, trimer, and tetramer (Newcomb... 

The nucleosidyl-3 -methylfluoridophosphonates (67) and (68) have been used for the synthesis of the corresponding methylphosphonate (69) and methyl-phosphonothioate (70) dimers respectively. The diastereomers (67) and (68) were prepared by phosphorylation of the corresponding 5 -protected nucleosides with (71) and for the latter mixture (68), separation of the individual diastereomers was possible using silica chromatography. Coupling of (67) and (68) with a 3 -0-protected nucleoside in the presence of DBU or sodium hydride gave over 95% yield of the respective dimers. 

The reaction of l,3,4-oxadiazin-2-one 91 with sodium hydride in tetrahydrofuran (THF) leads to an unprecedented Favorski-like ring contraction to form the 4,5-diphenylpyrazol-3-one 92, which then dimerizes with loss of one molecule of nitrogen to give 3,4,6,7-tetraphenyl-l,5-diazabicyclo[3.3.0]octa-3,6-dien-2,8-dione 93 (Scheme 11) <1996TL5039>. 

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