Alkenes, photoinduced alkylation

Pyrroles, furans and thiophenes undergo photoinduced alkylation with diarylalkenes provided that the alkene and the heteroaromatic compound have similar oxidation potentials, indicating that alkylation can occur by a non-ionic mechanism (Scheme 20) (81JA5570). 

Dondi, D., Fagnoni, M., Molinari, A., Maldotti, A., and Albini, A. (2004) Polyoxotungstate photoinduced alkylation of electrophilic alkenes by cycloalkanes. Chemistry - A European Journal, 10, 142-148. 

Ryu, I., Muraoka, H., Kambe, N., Komatsu, M., and Sonoda, N. (1996) Group transfer carbonylations photoinduced alkylative carbonylation of alkenes accompanied by phenylselenenyl transfer. Journal of Organic Chemistry, 61, 6396-6403. 

Photoinduced Alkylation of Alkenes and Alkynes by Alkanes, Alcohols and Alkyl Halides... 

Figure 5.9. Functionalization of GaN using the UV-photoinduced reaction with alkenes. Using a shadow mask for the irradiation allows for patterned functionalization. In this study, the alkyl terminated layer was later functionalized with DNA. Figure reproduced with permission from Ref. [152]. Copyright...

It has been demonstrated that visible light irradiation of the absorption band of AcrH + in the presence of organometallic compounds and alkenes and alkylbenzenes in MeCN results in efficient C-C bond formation between these electron donors and AcrH+ via photoinduced electron transfer from the donors to the singlet excited state of AcrH+ to yield the alkylated or allylated adducts selectively [89-91], The AcrH+ is also photoreduced by ethylbenzene and other alkylbenzenes to yield the corresponding 9-substituted-10-methyl-9,10-dihydroacridine [92] ... 

Tetramethylammonium phenyl-trialkylborates in the photoinduced electron transfer reaction with benzophenone. Generation of alkyl radicals and their addition to activated alkenes. Tetrahedron Letters, 36, 5483-5486. 

From a synthetic point of view, bond forming steps are the most important reactions of radical ions [202]. Several principle possibilities have been described in Section 8.1 and are summarized in Scheme 52. Many carbo- and heterocyclic ring systems can be constructed by (inter- and intramolecular) radical addition to alkenes, alkynes, or arenes. Coupling of carbonyl radical anions leads to pinacols either intra-or inter-molecular which can be further modified to give 1,2-diols, acyloins or alkenes. Radical combination reactions with alkyl radicals afford the opportunity to synthesize macrocyclic rings. These radical ion-radical pairs can be generated most efficiently by inter- or intramolecular photoinduced electron transfer. 

In the absence of a strong acid, photoinduced electron transfer from RH (alkyl-benzenes [276] and alkenes [277]) to the singlet excited state of AcrH+ ( AcrH+ ) is reported to lead to formation of the alkylated or ally la ted adducts, 9-R-lO-methyl-9,10-dihydroacridine (AcrHR). Photoinduced electron transfer form a variety of organometallic compounds (RM) also gave the same type of adduct, AcrHR [278-282]. In the presence of HCIO4 (l.2 M), however, the photooxygenation of ethylbenzene to 1-phenylethanol occurs as shown in Eq. 26 ... 

In the next part, the recent results on the addition of >P(0)H species to unsaturated substrates are summarized. The photoinduced hydropho-sphinylation of alkenes with diphenylphosphine oxide afforded substituted alkyl-diphenylphosphine oxides (Scheme 21). ... 

The facile photosensitized oxidation of tetraalkylstannanes (R4 n) and related group-14 compounds has been widely exploited by Mella and co-workers to form carbon-centered radicals. Photoinduced electron transfer from tetraalkylstannanes to a sensitizer, such as aromatic nitriles and esters (including tetramethyl pyromellitate, TMPM), affords a radical cation [R4 n] that can fragment to form an alkyl radical (R) together with the R3Sn+ cation. The alkyl radicals can then react with electron-poor alkenes, alkynes, aromatics, or the radical anion formed from the photosensitizer to form new carbon-carbon bonds. Careful choice of the photosensitizer can ensure that the radical anion selectively reduces the radical adduct (derived from addition to a double bond) rather than the first-formed alkyl radical (Scheme 5). 

A variety of photoinduced electron transfer reactions leading to the alkylation of heteroaromatic compounds are known. A typical example involves the reaction of five-membered heterocycles with electron-rich alkenes as illustrated in Scheme 9 Thus, photolysis of furans in the presence of 1,1-diarylethenes and a sensitizer (such as 1-cyanonaphthalene) gives alkylated products in good yield following an unusual... 

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