Pyrex filtered light

A -Bridgehead compounds have been obtained from the photochemical cyclization of cfi-1-styrylimidazoles. For example, irradiation of the imidazole (532) in methanol in the presence of I2 resulted in cyclization at the 2-position of the imidazole ring with the formation of an imidazo[2,l-a]isoquinoline (533) (76JCS(Pl)75). Isomerization of the trans-to the c/i-styrylimidazole was followed by photodehydrocyclization, trans- 1-Styrylbenzimidazole (534) was isomerized under Pyrex-filtered light in the presence of one molar equivalent of I2. The resulting cis isomer on irradiation through quartz gave the benzimidazo[2,l-a]isoquinoline (535) in 53% yield. 

For example, when a solid solution of o-[38a] in 2-MTHF was irradiated with Pyrex-filtered light in an esr cavity at 11 K, a set of intense esr signals was obtained as shown in Fig. 22. The spectrum as a whole resembles that of See the Appendix on p. 245 of suffixes to structural formula numbers. 

No reaction occurs between CF3SCI and CO within 8 hr at 100°C. However, on irradiation of a mixture of CFjSCl and CO with Pyrex-filtered light (A >300 nm), predominantly CFsSSCFg and COCI2 are formed, as well as minor amounts of CFgS—C(0)C1 157). 

Perfluoro(hexaethylbenzene) (24), which has low solubility in all common solvents, has been irradiated as a suspension in perfluoropentane.23,24 After irradiation for 15 days, much of the material had gone into solution. The product mixture contained starting benzene 24 (33%), prismane 26 (64%), and Dewar benzene 25 (3%).24 Irradiation of 24 for 69 days using a Pyrex filter (light at > 270 nm) resulted in 4% recovery of benzene 24 and 96% of Dewar benzene 25.24 None of the corresponding benzvalene isomer was detected after irradiation with either filtered or unfiltered light. 

Solid samples placed in the bottom of the test tube were cooled in a cooling apparatus and were irradiated by Pyrex-filtered light transmitted by using a flexible light guide from a 250-W ultra-high-pressure mercury lamp. When the powdered lb was irradiated at 15 °C for 2 h, a quantitative amount of 3-(7V-methylaniliiio)-3-phenylphthalide 2b ( 11521 (c 1.0, CHCI3)) was obtained. 

Monolayer dry solid assemblies of the starting [82, 83] complexes pyrex-filtered light Ru(DOEPIX)(py) stable in vacuo in the presence of L (CO, N2, 02, py), Ru(DOEPIX)(py) forms Ru(DOEPIX)(py)L ... 

Figure 7 includes UV spectra of the crystals of thioesters 57a-c, indicating the molecules absorbed photons sufficiently in the solid-state beyond 290 nm (Pyrex filtered light). Irradiation of powdered (+)-57a at 0°C led to production of 3-phenyl-3-(o-tolylthio)phthalide 58a as a major product in 65 % yield with complete consumption of the starting material. As expected, the asymmetric generation in 58a was realized by an observation of its specific rotation which was +37° which corresponded to 30% ee. 

The photochemical rearrangement of azavinylcydopropane 125 also occurs [60] readily to produce 1-pyrroline derivatives 126 in high yield (50-85%) upon irradiation using Pyrex-filtered light, as shown in Scheme 8.36. 

In addition, oxidative photocyclization has been applied for the formation oftetra-, penta-, and hexa-cyclic azonia-aromatic compounds via photoinduced quaternization (Scheme 9.22). In order to avoid photodecomposition of the photoproduct, the substrates are irradiated selectively by using Pyrex-filtered light through an aqueous nickel sulfate solution filter [33]. 

Dias and co-workers 48, 48a) investigated the photochemistry of the complexes MoCp2(CH3)2 48) and [MCp2(CH3)2]PF6 (M = Mo or W) 48, 48a) and found that only the cationic complexes were photosensitive. Irradiation of MoCp2(CH3)2 with pyrex-filtered light (A > 310 nm) led to no detectable reaction. However, irradiation of the complexes [MCp2(CH3)2] in the presence of added donor ligands led to photopro-... 

The vagaries of photosubstitution are nicely illustrated by the reactions of 1-methoxy-2-fluoro-4-nitronaphthalene. It undergoes reaction at each of the three substituted positions in the presence of Pyrex filtered light. Substitution takes place at position 1 in the presence of sodium hydroxide in acetonitrile-water, at position... 

Photolysis is a particularly effective and convenient way to promote substitution. Arenes containing various leaving groups react with acetone enolate ion at —33° under the stimulation of Pyrex filtered light to give phenylacetone in yields which sometimes are nearly quantitative. The reactivity order in terms of leaving groups is... 

The primary photochemical product formed from the irradiation of the 2-thiones (115) in the presence of alkenes is the oxetanes (116). The reaction conditions use Pyrex filtered light in benzene solution. Under these conditions the initial product is unstable and reacts further either by C-O or C-S bond fission which leads to the isolated products (117) and (118) in the yields shown. 

Reactions of 1,3-Diketones - The carboximide derivative (203) undergoes photochemical rearrangement on irradiation in acetonitrile using Pyrex filtered light. The reaction is considered to proceed by a zwitterionic intermediate such as (204). When the reaction is carried out in the presence of P-ketoesters [e.g. (205)] with added triethylamine, adducts are formed in yields of 40-60% and have been identified as (206). The intermediacy of (204) is supported by the formation of (207). 

The photochemical decomposition of several dioxolane derivatives (234) has been reported. The reactions are brought about in cyclohexane with Pyrex-filtered light and the work is aimed at producing protected derivatives of aldehydes that can be liberated by photolysis and uses the well-established hydrogen abstracting power of a photoexcited o-nitro group. ... 

Z)-But-2-ene (6.3 g, 0.11 mmol) was condensed into a tube containing 4-tolyldiazomethane (95 mg, 0.72 mmol) and benzophenone (750 mg, 4.1 mmol). After sealing, the tube was irradiated with Pyrex-filtered light from a 450-W Hanovia medium-pressure Hg vapor lamp for 2 h. The solvent was removed under vacuum and the product was isolated by distillation. Total yield of products 92 mg (80%). Other examples b-d are also given. 

A solution of the appropriate aryldiazomethane (60-80 mg) in 1,1-dimethylallene (ca. 7 mL) was freeze-degassed and sealed in a Pyrex tube at 0.1 Torr. The tube was irradiated with Pyrex-filtered light from a 450-W Hanovia medium-pressure source until the diazomethane color disappeared (ca. 3 h). The solvent was removed under reduced pressure and the product mixture was isolated by distillation at 0.05 Torr. Many arylcarbenes have been added to 1,1-dimethylallene using this procedure. - " The results reported in detail are summarized in Table 3. 

Conversion of 1,1-dihalocyclopropanes to monohalocyclopropanes has also been carried out photochemically using mercury lamps filtered through quartz or Pyrex. ° Acetone sensitized photolysis using Pyrex-filtered light results in the cleanest reaction mixtures. For example, the photolysis of dibromo compounds 49. o-i72... 

Irradiation of a solution of pentacarbonyl[(cyclopropyl)(3-methylbut-3-enoxy)carbene]chro-mium(O) in diethyl ether in the presence of carbon monoxide with Pyrex-filtered light gave l-cyclopropyl-5-methyl-2-oxabicyclo[3.2.0]heptan-7-one in 65% yield. ... 

Experimental details.1556 An aqueous solution of an amide (0.2 m, 10 ml) was irradiated with Pyrex filtered light from a high pressure mercury lamp (200 W) (Figure 3.9) in the presence of suspended unreduced anatase (Ti02 100mg) under a constant stream of oxygen. Products were isolated using preparative GC. 

The cyclopropene (90a) undergoes dimerization to (91) when irradiated in benzene or hexane with Pyrex-filtered light. When the irradiation was carried out in the presence of a triplet quencher the dimerization product is absent and a new product (92a) is formed. A bicyclohexene (92b) is also formed from the irradiation of the cyclopropene (90b). The authors suggest that the most likely route to these products is via an intermediate carbene (93). Further evidence for the existence of the carbene was obtained by trapping experiments in methanol... 

The enones (68) can be induced to cyclize to (69) using Pyrex-filtered light when BF3-Et20 is added to the system.39 An attractive mechanistic rationalization would involve a Cope process but this was excluded by the failure of the enol ether (70) to cyclize. This system undergoes cis-trans-isomerization, which is an efficient method of excited-state relaxation in these systems since the enone... 

The c/s-enone (159) undergoes cfc-fra/zs-isomerization by irradiation of a degassed solution in benzene using Pyrex-filtered light.92... 

Reduction of halides is a useful application of this process and there are variations that make it more useful. Mariano and co-workers showed that the bromide in 591 is removed to give a radical, and this cyclizes (via 592) in the presence of the enaminone moiety to give a mixture of several products on irradiation with Pyrex filtered light.6i3 When a Vycor filter (secs. II.IO.B and sec. 13.4) was used to limit the incident light to >220 nm [130 kcal mol 1, 544.2 kJ mol l] (required for the enaminone moiety), radical cyclization was the major process (sec. 13.7 for a discussion of radical cyclization), giving 593 in 85% yield. 

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