Toluene irradiation

Table 4.27. Quantum Yields of E Z Photoisomerization of Indolyl Fulgides 85 in Toluene (Irradiated at 405 nm) ...

Figure 5 shows the growth of fluorescence from biphenyl ((j)2) in toluene irradiated by fine structure pulses of 30-ps duration. The observed fluorescence is produced by energy transfer from the excited solvent state T to biphenyl. 

Ishikawa and co-workers (50, 51) have also reported the photodegradation of backbone disilane polymers (Scheme III). In this case, as in the previous example with pendant silyl substituents, silicon-silicon bond homolysis to produce silyl radicals was the predominant process. When irradiated in toluene, the photodegraded polymer showed a substantial -SiH band at 2150 cm in the IR spectrum. Similarly, NMR spectroscopic examination of the irradiated polymer showed evidence of silyl radical substitution into the solvent toluene. Irradiation of the polymeric disilane in deuterated methanol produced no bands due to Si-D in the IR spectrum and resulted in the incorporation of the elements of methanol into the chain ends (as revealed by NMR spectroscopy). For the phenyl-substituted polymer, the NMR evidence indicated that <5% of rearranged cyclohexadiene derivatives were formed. 

The rearrangement of 15 to 9 was performed in most cases in refluxing benzene or toluene irradiation also effected the dinitrogen extrusionThe use of the silyl azides (18)90.119 Qj. 1990 allowed the preparation of 9 or the corresponding aminocyclopropane in a one pot procedure starting from the acid chloride or acid anhydride. A cyclopropyl isocyanate (9) also could be obtained directly from the carboxylic acid, triethylamine and diphenylphosphoryl azide (17) ... 

A soln. of 3-oxo-ll/ -nitrosyloxy-20-hydroxy-20-cyano-zl -pregnene in toluene irradiated 25 min. at 20° under Ng with a high-pressure Hg-lamp 3,20-dioxo-ll/ -hydroxy-lS-cyano-zl -pregnene. Y ca. 30%. - Photolysis of the nitrile group initiates the nitrile group migration. F. e. s. J. Kalvoda and L. Botta, Helv. 55, 356 (1972). 

Experimental data taken from the chlorination of toluene in a continuous stirred tank flow reactor at 111°C and irradiated with light of 500 nm wavelength yield a product distribution shown in Table 1 (1). 

Compound 6 is a pivotal intermediate in Schreiber s synthesis. It was hoped that the conspicuous and strained bridgehead cyclobutene substructure in 6 would undergo a conrotatory electrocyclic ring opening upon thermolysis to give an isomeric 1,3-diene (8, Scheme 1). In the event, when a solution of cyclobutene 6 in toluene is confined to a sealed tube and heated to 180°C for 12 h, a stereoisomeric mixture of 1,3-dienes 7 and 8 is produced in an excellent yield of 95% (7 8 ca. 5 1). Finally, irradiation of the 5 1 mixture of cis-7 and trans-8, or of each independently, establishes a photostationary state in which the desired trans isomer 8 predominates (8 7 ca. 10 1). 

The productive transformation of a macrocycle to a bicycle can also be executed simply by irradiating a bis(thiolactone). For example, irradiation of a solution of bis(thiolactone) 24 in toluene for... 

Method A A solution of the azidoquinoline (5 mmol) in 3M KOMe in MeOH (40 mL) and dioxane (40 mL) was irradiated under N2 using a water-cooled, 125-W medium-pressure Hg lamp until all the azide [as measured by the disappearance of u(N3) at 2120 cm" 1 or by TLC] had reacted (4-10h). The photolysate was left to stand at 20 C for 24h then neutralized cautiously by the addition of 4M IICI in MeOH. The solvent was removed under reduced pressure and the crude product was purified initially by column chromatography on alumina (Type H, toluene), then finally by crystallization (petroleum ether). 

Morrison and Migdalof (Ref 14) irradiated o-nitrotoluene and p-nitrotoluene with a Pyrex-filtered mercury lamp using D20 and p-dioxane as solvents. C-D bonds formed with o-nitrotoluene, with no C-D formation for p-nitro-toluene - ... 

The mechanism of cycloaddition reaction of maleic anhydride with anthracene promoted by US irradiation has been the subject of many controversies [32, 37]. Recent work of Da Cunha and Garrigues [35] shows that the reaction proceeds in toluene solution in the 60 85 °C temperature range in 6 3 h. 

Thus irradiation of benzophenone in toluene gives the photoreduction product 19, benzpinacol, and bibenzyl [equation (59)] of which only 19... 

In weaker acid systems, other reactions involving the triplet state supervene to the exclusion of dimerization. Photolysis of 85 in 3-3% sulfuric acid, 96-5% acetic acid, and 0-2% water gave as products tri-phenylmethane (93), 9-phenylfluorene (94), 6is-9-phenylfluorenyl peroxide (95) and benzophenone (96). When benzene was present, tetra-phenylmethane (97) was also formed in addition to the other products. When the triphenylmethyl cation is irradiated in 3-3% H2SO4, 80 1% HOAc, 16-4% toluene, and 0-2% H2O, the products observed were... 

Microwave irradiation has been used to accelerate the Gewald reaction for the one-pot synthesis of N-acyl aminothiophenes on solid support [67]. A suspension of cyanoacetic acid Wang resin 35, elemental sulfur, DBU and an aldehyde or ketone 36 in toluene was irradiated for 20 min at 120 °C in a single-mode microwave synthesizer (Scheme 13). Acyl chloride 37 was added, followed by DIPEA, and the mixture was irradiated for 10 min at 100 °C. After cooling to room temperature, the washed resin was treated with a TEA solution to give M-acylated thiophenes 38 in 81-99% yield and purities ranging from 46-99%. 

The rapid synthesis of 4-thiazolidinones by the MCR of an amine, aldehyde and mercaptoacetic acid has been developed under microwave-assisted conditions [73-75]. Irradiation of the three components in ethanol at 120 °C in the presence of molecular sieves [73] or in toluene at reflux under atmospheric conditions [74] in a single-mode microwave synthesizer gave the... 

Another interesting scavenger is polymer-supported anthracene, developed by Porco for the scavenging of dienophiles [109]. An example of its application to the synthesis of a complex 5,8-dihydro-(l,2,4)triazolo[l,2-a]pyridazine-l,3-diones via hetero-Diels-Alder reaction followed by removal of the excess of triazole-3,5-dione under microwave irradiation is depicted in Scheme 24. For this particular example, moving from thermal heating (toluene, 100 °C) to a microwave-assisted protocol (DCE, 150 °C) reduced scavenging time from 3 h to just 15 min. 

Rapid aminations of 1-bromonaphthalenes with piperidine under microwave irradiation were reported by Hamann using Pd2(dba)3/rac. PPFA (N,N-dimethyl-1-[2-(diphenylphosphanyl)ferrocenyl]ethylamine) precatalyst in combination with NaO-t-Bu in toluene at 120 °C (Scheme 92) [97]. Typically, reactions performed under conventional heating at 120 °C (oil bath) were still progressing after 16 h and were essentially complete by 24 h, whereas the microwave reactions appeared to be finished after 10 min. The same reaction conditions were also useful to functionalize 5- and 8-bromoquinolines with anilines and aliphatic amines (Schemes 93 and 94). Remarkably, no product formation was observed with 5-bromo-8-cyanoquinoline and 5-bromo-8-methoxyquinoline under conventional heating for 24 h at the same temperature, while the desired 5-aminoquinolines were smoothly obtained under microwave irradiation in a reaction time of only 10 min. 

The application of 1,3-dipolar cycloaddition processes to the synthesis of substituted tetrahydrofurans has been investigated, starting from epoxides and alkenes under microwave irradiation. The epoxide 85 was rapidly converted into carbonyl ylide 86 that behaved as a 1,3-dipole toward various alkenes, leading to quantitative yields of tetrahydrofuran derivatives 87 (Scheme 30). The reactions were performed in toluene within 40 min instead of 40 h under classical conditions, without significantly altering the selectivi-ties [64]. 

A family of interesting polycychc systems 106 related to pyrrolidines was obtained in a one-pot double intermolecular 1,3-dipolar cycloaddition, irradiating derivatives of o-allyl-sahcylaldehydes with microwaves in toluene for 10 min in presence of the TEA salt of glycine esters [71]. A very similar approach was previously proposed by Bashiardes and co-workers to obtain a one-pot multicomponent synthesis of benzopyrano-pyrrolidines 107 and pyrrole products 108 (Scheme 37). The latter cycloadducts were obtained when o-propargylic benzaldehydes were utihzed instead of o-allyhc benzalde-hydes, followed by in situ oxidation [72]. 

The Bischler-Napieralski reaction has been described to proceed imder microwave irradiation to give very good yields of dihydroisoquinolines [140] and other polycyclic compounds (see below) in the presence of POCI3 and P2O5 (classical conditions) in toluene (10 cycles of 60 s each using a dedicated microwave reactor). 

The same kind of results were obtained using the ionic hquid [bmim] [PFg ] as the medium to carry out the reaction in the presence of TEA at 60 °C for 30 s under microwave irradiation [151,152]. Toluene can be also used as the solvent as well TEA as the acid [153]. Heating at 60 °C for a longer period also allowed the reaction of different ketones, thus increasing the potential of the reaction for the generation of molecular diversity around a tricycUc scaffold such as 236 in Scheme 87. 

---