Diazo compounds ethers

The synthesis of thiepins 14 was unsuccessful in the case of R1 = i-Pr,79 but if the substituents in the ortho positions to sulfur arc /erf-butyl, then thiepin 14 (R1 = t-Bu R2 = Me) can be isolated in 99% yield.80 Rearrangement of diazo compound 13 (R1 = t-Bu R2 = H), which does not contain the methyl group in position 4, catalyzed by dimeric ( y3-allyl)chloropalladium gives, however, the corresponding e.w-methylene compound. The thiepin 14 (R1 = t-Bu, R2 = H) can be obtained in low yield (13 %) by treatment of the diazo compound with anhydrous hydrogen chloride in diethyl ether at — 20 C.13 In contrast, the ethyl thiepin-3,5-or -4,5-dicarboxylates can be prepared by the palladium catalysis method in satisfying yields.81... 

In 1988 Masoud and Ishak demonstrated that ( -arenediazo methyl ethers do not react with 2-naphthol in dry organic solvents such as dioxan, ethanol, 2-propanol, but only in the presence of water. The reactions are catalyzed by hydrochloric acid (even in the absence of water). Under such conditions almost quantitative yields of azo compounds were obtained. A careful and extensive kinetic investigation of the HCl-catalyzed dediazoniation of substituted benzenediazo methyl ethers, varying the HC1 concentration and the diazo ether/2-naphthol ratio (the latter either absent or in large excess), and comparing the observed rate constants with Hammett s acidity functions for dioxane and ethanol (see Rochester, 1970) indicated the mechanism shown in Schemes 12-8 to 12-10 (DE = diazo methyl ether, D+ = diazonium ion). 

Reaction with alcohols is general for diazo compounds, but it is most often performed with diazomethane to produce methyl ethers or with diazo ketones to produce ot-keto ethers, since these kinds of diazo compounds are most readily available. With diazomethane the method is expensive and requires great caution. It is used chiefly to methylate alcohols and phenols that are expensive or available in small amounts, since the conditions are mild and high yields are obtained. Hydroxy compounds react better as their acidity increases ordinary alcohols do not react at... 

Amides can also be alkylated with diazo compounds, as in 10-49. Salts of sulfonamides (ArS02NH ) can be used to attack alkyl halides to prepare N-alkyl sulfonamides (ArS02NHR) that can be further alkylated to ArS02NRR. Hydrolysis of the latter is a good method for the preparation of secondary amines. Secondary amines can also be made by crown ether assisted alkylation of F3CCONHR (R = alkyl or aryl) and hydrolysis of the resulting F3CCONRR. ... 

The readily accessible dibenzothiapyrylium salt (62)m reacts with ethyl lithio diazoacetate 47) in a 1 1 mixture of ether and tetrahydrofuran at —120 °C to form the diazo compound (65). Treatment of 65 with 5 mol-% of it-allylpalladium chloride dimer in a 1 2 mixture of chloroform and carbon tetrachloride at 0 °C and... 

On standing, diphenyldiazomethane decomposes to yield benzophenone azine. In one of the checkers runs the product was stored at room temperature after 2 days, crystals of the azine were visible. The product at this stage was assayed by treatment with benzoic acid addition of 6.8 g. of the diazo compound in a thin stream to a solution of 17 g. of benzoic acid in 90 ml. of ether, and, after 30 minutes, extraction of the excess benzoic acid with dilute sodium hydroxide followed by distillation of the ether, gave 7.4 g. (75%) of crude benzohydryl benzoate melting at 83-85°. In the same procedure the freshly prepared diazo compound gave a quantitative yield of the crude ester. 

The common by-products obtained in the transition-metal catalyzed reactions are the formal carbene dimers, diethyl maleate and diethyl fumarate. In accordance with the assumption that they owe their formation to the competition of olefin and excess diazo ester for an intermediate metal carbene, they can be widely suppressed by keeping the actual concentration of diazo compound as low as possible. Usually, one attempts to verify this condition by slow addition of the diazo compound to an excess (usually five- to tenfold) of olefin. This means that the addition rate will be crucial for the yields of cyclopropanes and carbene dimers. For example, Rh6(CO)16-catalyzed cyclopropanation of -butyl vinyl ether with ethyl diazoacetate proceeds in 69% yield when EDA is added during 30 minutes, but it increases to 87 % for a 6 h period. For styrene, the same differences were observed 65). 

Dimethyl-l-phenylpropenylidene (15) was generated from the tosylhy-drazone sodium salt 11 as well as from 3,3-dimethyl-5-phenylpyrazole (12), by way of the diazo compound 14.17,18 The reaction of 15 with methanol gave a mixture of the isomeric ethers 18 and 19, pointing to intervention of the allylic cation 16 (Scheme 7). In order to assess the regioselectivity of 16, the solvolysis of the 4-nitrobenzoate in methanol was also studied. Although 19 prevailed in each case, the 19 18 ratio obtained from 11 (1.5) and from 12 (1.7) was inferior to that obtained from 13 (5.1). 

Enol ether additives were used to probe the protonation of 3-cyclopen-tenylidene (127). Treatment of A-nitroso-A-(2-vinylcyclopropyl)urea (124) with sodium methoxide generates 2-vinylcyclopropylidene (126) by way of the labile diazo compound 125 (Scheme 25). For simplicity, products derived directly from 126 (allene, ether, cycloadduct) are not shown in Scheme 25. The Skat-tebpl rearrangement of 126 generates 127 whose protonation leads to the 3-cyclopentenyl cation (128). In the presence of methanol, cyclopentadiene (130) and 3-methoxycyclopentene (132) were obtained.53 With an equimolar mixture of methyl vinyl ether and methanol, cycloaddition of 127 (—> 131)... 

By very careful hydrogenation (with stannous chloride in ethereal hydrogen chloride) phenyl azide has been converted into the exceedingly sensitive phenyltriazene (Dimroth), which, as has been shown, can be reconverted into the former by dehydrogenation. As in the case of the aliphatic diazo-compounds, an open chain structural formula has lately also been assigned to hydrazoic acid and its esters, so that the changes just mentioned may be formulated as follows ... 

Even the doubly unsaturated hydrocarbons, such as butadiene, can be coupled with suitable diazo-compounds. Finally, not only phenols, but also phenol ethers, such as anisole, are capable of coupling (K. H. Meyer1). 

The catalytic activity of rhodium diacetate compounds in the decomposition of diazo compounds was discovered by Teyssie in 1973 [12] for a reaction of ethyl diazoacetate with water, alcohols, and weak acids to give the carbene inserted alcohol, ether, or ester product. This was soon followed by cyclopropanation. Rhodium(II) acetates form stable dimeric complexes containing four bridging carboxylates and a rhodium-rhodium bond (Figure 17.8). 

Laser flash photolysis of phenylchlorodiazirine was used to measure the absolute rate constants for intermolecular insertion of phenylchlorocarbene into CH bonds of a variety of co-reactants. Selective stabilization of the carbene ground state by r-complexation to benzene was proposed to explain the slower insertions observed in this solvent in comparison with those in pentane. Insertion into the secondary CH bond of cyclohexane showed a primary kinetic isotope effect k ikY) of 3.8. l-Hydroxymethyl-9-fluorenylidene (79), generated by photolysis of the corresponding diazo compound, gave aldehyde (80) in benzene or acetonitrile via intramolecular H-transfer. In methanol, the major product was the ether, formed by insertion of the carbene into the MeO-H bond, and the aldehyde (80) was formed in minor amounts through H-transfer from the triplet carbene to give a triplet diradical which can relax to the enol. 

Insertion of the carbenes, via a low-lying singlet state close to the ground-state triplet, generated by photolysis of the diazo compounds (128), into the CO bond of cyclic ether solvents (THF, THP, dioxane) gave rise to polyether-bridged azulenes such as (129). ... 

A -Unsubstituted 1,2,4-diazaphospholes (4) undergo A -alkylation by reaction with alkyl vinyl ether, sulfur ylides, and diazo compounds <95HAC403>. They react with acyl chlorides in a 2 1 molar ratio to give a mixture of the A -acylated diazaphosphole and the diazaphosphole hydrochloride. Preparative A -acyclation is achieved in presence of a tertiary amine. Sulfonyl chlorides and phosphorus trichloride also give A -substitution reactions (Scheme 2) <87TH 422-01 >. 

The preparation of thiiranes is most conveniently performed in solution. However, there are also protocols reported for reaction in the gas and solid phase. By using diazo and thiocarbonyl compounds in ether as solvent, both alkyl and aryl substituted thiiranes are accessible. As indicated earlier, aryl substituents destabilize the initially formed 2,5-dihydro-1,3,4-thiadiazole ring and, in general, thiiranes are readily obtained at low temperature (13,15,35). On the other hand, alkyl substituents, especially bulky ones, enhance the stability of the initial cycloadduct, and the formation of thiiranes requires elevated temperatures (36 1,88). Some examples of sterically crowded thiiranes prepared from thioketones and a macro-cyclic diazo compound have been published by Atzmiiller and Vbgtle (106). Diphenyldiazomethane reacts with (arylsulfonyl)isothiocyanates and this is followed by spontaneous N2 elimination to give thiirane-2-imines (60) (107,108). Under similar conditions, acyl-substituted isothiocyanates afforded 2 1-adducts 61 (109) (Scheme 5.23). It seems likely that the formation of 61 involves a thiirane intermediate analogous to 60, which subsequently reacts with a second equivalent... 

Second, the formation of the diazobenzazocine derivatives 264a-e represents an unprecedented reaction for intramolecular 1,3-dipolar cycloaddition reactions of diazo compounds. Note that diazo compounds such as 247a (305) and 248 (307) also give bridged diazabicyclo[n.2.1]alkenes rather than fused diazabi-cyclo[ .3.0]aUcenes upon treatment with Bp3-etherate, but these transformations... 

The mixture of 5 and 6 can be converted to 9 by reduction, separation and then epimerization/reduction of one isomer. Alcohol 9 is then further subjected to similar procedure as for 1 to give tricyclic ether 12, through the same Cu(tfacac)2-catalyzed ylide formation/[2,3]-sigmatropic rearrangement of diazo compound 10 (Scheme 2). 

Similar reactions are probably involved in the carbonylation reactions of oximes (80), oxime ethers (S3), nitriles (81), and of diazo compounds (53). 

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