Acetylene photoaddition

Photoaddition of acetylene, 349 Photoaddition of allene, 349 Photoaddition of dichloroethylene, 349 Photoaddition of ethylene, 348 Photoaddition of hexafluoroacetone, 345 Photoaddition of maleic anhydride, 348 Photochemical addition of ethylenes and acetylenes to steroidal enones and dienones, 343... 

Additions to Aromatic Hydrocarbons. A variety of photochemical additions to aromatic hydrocarbons have been reported. Benzene and its derivatives add to maleic anhydride74-76 as well as to simple olefins,77-80 isoprene,81 acetylene derivatives,79,82 and alcohols.83 The mechanism of the maleic anhydride-benzene reaction is discussed in Section IV. A.4. Naphthalene forms a photoadduct with dimethyl acetylenedicarboxylate62 and with acrylonitrile8211 while anthracene behaves similarly with maleic anhydride84 and with 1,2-benzanthracene.85 The photoaddition of several aromatic amines to anthracene has been reported to proceed via a charge transfer complex86,87 in fact, the majority of these addition reactions may proceed in this manner. 

The photoaddition of hydrogen bromide to olefines and acetylenes is used to synthesize alkyl and alkenyl bromides... 

Almost simultaneously, papers by Schmid et al.509 and by Gotthardt and Reiter510 appeared on the photoaddition of DMAD to sydnones the last authors also used propiolic and phenylpropiolic esters. Ohta et al.511 showed that similar reactions could be carried out with 3-alkyl-4-phenylsydnones, and other papers on the addition of acetylenic esters to sydnones have appeared.512-514... 

In the presence of trifluoroacetic acid, irradiation of dimethyl acetylenedi-carboxylate and benzene leads to the formation of dimethyl fumarate and dimethyl maleate in appreciable amounts in the absence of acid, only traces of these compounds were detected [36,61], Irradiation of dimethyl acetylenedicarboxylate and benzene in the presence of tetracyanoethylene (TCNE) produces a 1 1 1 adduct at the expense of cyclooctatetraene. The photoaddition still proceeds readily behind a fdter transmitting at wavelengths >290 nm, where only the acetylene absorbs to a significant degree [60],... 

Using the temperature effect, it was proven that non-emitting exciplex intermediates were also involved in the cycloaddition. For example, in the reaction of naphthalene with diphenylacetylene, with increasing temperature both the quantum yields of photoaddition and the quenching of the naphthalene fluorescence by acetylene decrease by the same magnitude [65],... 

Photochemical 27t-27t cycloaddition of benzo[l,2- 4,5-6 Jdithiophene and substituted acetylenes have been used to synthesize cyclobuta[6]thieno[2,3 /][I]benzothiophenes 103 <03JOC8258>. Both disubstituted acetylenes and diynes have been shown to undergo this type of 27t-27i photoaddition and moreover the addition was found to undergo via a syn addition. Photoirradiation of tris(2-benzo[6]thienylmethane) 104 in acetonitrile undergoes a di-7t-methane rearrangement to produce a cyclopropane, which upon further irradiation is easily converted to a secondary product, a thiopyran 105 <03TL751>. 

Cycloaddition of the acetylenes (215) to the non-conjugated diene (216) yields the cycloadducts (217). Thioesters (218) are formed by photoaddition... 

Photoinduced reactions of ethylenes and acetylenes with five-membered heteroarenes continues to be of interest to a number of groups. Mukai and co-workers have shown that 3-aryl-2-isoxazolines (65) undergo [2 r + 2 r] photoaddition to furan and thiophene to give the novel adducts (66) and (67), respectively. The reaction provides a further example of the rarely observed... 

In the photoaddition of a saturated hydrocarbon to ethyl propiolate (equation 19) it is likely that the excited state of the acetylenic ester initiates reaction by abstracting a hydrogen atom from the hydrocarbon. The addition of cyclic ethers to an alkyne seems similar (equation 20), although a ketone sensitizer is required for addition of tetrahydropyran or dioxan . When reactions of this type involve a conjugated acetylenic ester, the first-formed a,p-unsaturated ester can normally undergo further photochemical reaction to produce the p,y isomer (see equations 19 and 20). 

Alcohols can undergo photoaddition to alkynes, and the products from acetylenic esters are Y-hydroxy-rra//j-a,j3-unsaturated esters or the unsaturated lactones derived from the cis isomers by cyclization (equation 21). Reaction with acetylenic ketones provides a route to furans (equation 22) , and there is n.m.r. evidence for... 

In some systems an alcohol gives rise to photoreduction products of the alkyne rather than to products by photoaddition of the whole alcohol molecule. The acetylenic ester 13 gives the corresponding ethylenic ester on irradiation in methanol (equation 24). Under the same conditions the ketone (CH3)3C—C=C—COMe... 

Photodimerization of acetylene to give vinylacetylene (butenyne) and formation of polymers in the photolysis of alkynes generally are examples of photoaddition to alkynes. Photopolymerization of di- and poly-ynes has been studied, and for both conjugated diynes or triynes the polymerization process is a 1,4-addition reaction (equation 34). The products are highly unsaturated, and they tend to contain a high proportion of oxygen after exposure to the atmosphere. 

Under certain conditions ( — 78 °C, liquid phase) ethenethiol (CH2=CH—SH) is the major product of the photoaddition of hydrogen sulphide to acetylene . ... 

The cycloaddition of the allenes (63) to cyclopentenone results in the formation of the two adducts (64) and (65) in a ratio of 4 1. The addition reaction occurs primarily across the less substituted double bond of the aliens. Cycloaddition of acetylene and but-l-yne to the enones (66) can be brought about using left-circularly polarised light. The resultant cyclobutane derivatives are readily converted to the optically active enones (67). The photoaddition of hex-1-yne to the lactone (68) affords the two isomeric adducts... 

Photoaddition of acetylenes to benzene provides a convenient synthetic route to cyclooctatet-raenes through or//io-photocycloaddition. Although the meta cycloaddition would be a symmetry-allowed concerted process from Sj or Tj excited acetylene and S, benzene, or from Sq acetylene and Si (Bjn) benzene, there are surprisingly few reported cases in which an acetylene underwent weM-photoaddition to a benzene ring to give a semibullvalene. 

Die Photoaddition von Cyan-acetylen an Inden ergibt als Hauptprodukt 2-Cyan-2a,7a-dihydro-7H-(cyclobuta- a]-inden )i. 

Fur die Photoaddition von Isopropanol an Acetylen-Derivatc gibt es inzwischen Bclege die Ausbeuten der entstehcnden a,/ -ungesatt,igten Alkohole sind sohr unterschiedlich1-2 ... 

The tetracyclic compound 90, a photoaddition product of flavoquinone and acetylenic enzyme inhibitors, decomposes in alkali to give the highly fluorescent pyrrolo[l,2-a]quinoxaline 91." °... 

Two modes for the photoaddition of acetylene to the cholestenone (74) have been reported. Thus [2 + 2]-cycloaddition yields the adducts (75) and (76) whereas an ene-type addition yields the ethylidene derivative (77). 

The u.v.-induced addition of propan-2-ol to acetylene has been studied with and without acetone as sensitizer.168 The acetylene (241) undergoes photoaddition of isopropylamine and isopropyl ether to yield (242) and (243a) respectively.16 The same acetylene also reacts with ethyl 2-methylpropionate giving /rans-(243b) and the cyclic product (244). 

All the previously reported examples of photoaddition of acetylenes to benzene involve 1,2-cycloaddition and subsequent formation of cyclo-octatetraenes10 (but see ref. 43 for a discussion of the addition of perfluorobut-2-yne to benzene). The report of 1,3-cycloaddition of diphenylacetylene to the trimethyl ester of trimesic acid, is, therefore, of interest as this leads directly to the semibullvalene system.44 The reaction apparently requires 6 days, the yield of the product is low, and the adduct (28) is not isolable in the pure state. The triethyl ester and the acetylene also yield (29) via a stilbene-phenanthrene cyclization of the primary... 

When acetylenes are irradiated in aqueous solution [27], in acetic acid [28], or in alcohols [29,30], photoaddition reactions take place to give a ketone, an enol acetate, or an enol ether, respectively. In the photohydration reaction, a hydrated proton attacks the singlet excited state of the acetylene directly [31], On the other hand, alcohols give addition products by attack on the excited states of acetylenes in a radical-like mechanism. Radical photoaddition to acetylenes occurs also with saturated hydrocarbons such as cyclohexane [29], and with cyclic ethers such as tetrahydrofiiran [32], Simple acetylenes are photoreduced on irradiation in hydrocarbon solvents for example photolysis of dec-l-yne or dec-5-yne in pentane gives the corresponding alk-ene (dec-l-ene or trans- and ds-dec-5-enes) [32]. 

Neutral carbon of organic compounds is inherently a very weak base due to the lack of nonbonding electrons. However, the 7r-system of alkenes, alkynes, and allenes are potential basic sites due to the availability of 7t-electrons. Wooldridge and Roberts [61] first reported the facile photohydration of arylacetylenes to the corresponding ketones (in an overall Markownikoff sense) in dilute aqueous acid solutions. The facile protonation of the excited state was attributed to the enhanced basicity of the alkyne moiety in the excited state, more specifically as a result of extensive charge migration from the aryl group to the acetylene moiety. The photoaddition of methanol [62] and acetic acid to 7c-electron systems such as alkenes, alkynes, and allenes may be rationalized in the same way. 

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