Allenes photochemical reactions

Am. Chem. Soc. 1993, 115, 459—466 for some leading references on modern photochemical reactions of allenes, see... 

The photochemical reaction of diiron //-alkcnylidc complexes with diazo compounds leads to -allene complexes, which can be cleaved by several methods to yield allenes, for example allenic esters [32]. 

Photochemical reactions of quinones with allenes have also been studied and in some cases cyclobutane formation occurs, although in competition with products derived from attack of the allene on the carbonyl oxygen. Thus, photocycloaddition of tetramethyl-l,4-benzoquinone with 1,1-dimethylallene affords the four-membered carbocycle 6 in good yield.12... 

During the course of these investigations, the thermal and photochemical reactions of [Mn2(CO)10] with allene and some substituted allenes have been studied, but with no positive results. However, when the photochemical reaction is conducted with allene (129a) at reduced temperatures, three products can be isolated from the reaction mixture [Eq. (69)]. The yellow complex n-rj2 2-alleneoctacarbonyldimanganese(0) (130a) predominates, and in addition the by-products octacarbonyl- i- 3 3-tetramethyleneethanedi-... 

Thermal or photochemical reactions of allene episulfide do not appear to have been reported in the period 1996-2006. 

Intramolecular Additions - The predominant photochemical reaction of the allene derivatives (65) is (2 + 2)-cycloaddition yielding the housanes (66). The reaction occurs in a variety of solvents (e.g. hexane, acetonitrile or acetone) and the triplet excited state of (65) is implicated. In hexane and... 

Photochemical Reactions. The addition of allene to a steroidal enone on AI2O3 revealed a reversal of stereochemistry to that observed in solution [41] (Scheme 13). 

The irradiation of the methyl substituted cyclic allene (163) has been studied to evaluate the influence of substitution on the reactions encountered. This work follows on an earlier study of the photoreactivity of the unsubstituted allene. Direct irradiation using light of wavelength > 220nm in pentane brought about the formation of the products shown in scheme 7 in the yields shown below the appropriate structure. The products obtained from this reaction were compared with those from a thermally generated carbene intermediate and the conclusion reached is that carbene intermediates are involved in the photochemical reaction. This is different from the unsubstituted case 80... 

The acetophenone-sensitized photochemical reactions of allene have been interpreted in terms of non-vertical energy transfer to produce the planar allene triplet. 8 Several products are formed in the reaction, among which are allene dimers and trimers. Two ketones are also obtained, one (86) of which arises by attack of the central carbon of the allene triplet on the ortho-position of the acetophenone. 

Other dimerizations initiated by acetylene-allene interconversions have also been reported, and dimerization has also been applied to other cumulenes. The structure of the solid-state photodimer of tetraphenylbutatriene has now been reassigned, the new bis-allene structure (251) proposed being substantiated by ozonolysis to the known diketone (252), and by X-ray analysis. The solid-state photochemical reaction thus contrasts with the thermal dimerization, which gives the radialene (253). ... 

Photochemical Reactions with Alkoxychromium Carbene Complexes. Photolysis of chromium alkoxycarbene complexes in the presence of tosylmethylene phosphorane [or ester stabilized ylides such as (methoxycarbonylmethylene)-triphenylphosphorane] under an atmosphere of carbon monoxide produced aflenes. Such reactive allenes (EWG at C1 and electron donating group at C3) hydrolyzed to give y-keto-a. -unsaturated sulfones with. stereoselectivity (eq 6). ... 

McKellar and Allen have reviewed the photochemical reactions taking place in commercial polyolefins. 

CpFe(CO)2] anions (Fp anions) also react with allenic electrophiles in an Sn2 fashion to generate Fp-substituted 1,3-dienyl complexes.Thermal and photochemical reactions with these Fp complexes result in the formation of 77 -butadienyl complexes. 

N. S. Allen and J. F. McKellar, Photochemistry of Dyed and Pigmented Polymers , Applied Science Publishers, London, 1980 J. F. Rabek, Mechanisms of Photophysical Processes and Photochemical Reactions in Polymers Theory and Applications , Wiley, Chichester, 1987. 

AUenes are frequently used as building blocks for the synthesis of cychc compounds by inter- and intramolecular photochemical cycMzation reactions with ketones, thiones, enones, and related compounds. Most of the reactions, however, proceed between the ground state of the allenes and the excited state of the other reactants. Over the past 40 years, many photochemical reactions of allenes have been reported, and theoretical studies of the excited states have been conducted. " In this chapter, the fundamental photochemical reactions of allenes will be described. 

Fujita and co-workers reported the photochemical reaction of allenes in acetic acid. Irradiation (254 nm) of 14a-e affords the respective enol acetates 15. In the reaction of 14b, a triplet mechanism is proposed on the basis of quenching experiments. In methanol solution, on the other hand, the photochemical reaction of tetraphenylaUene 16, using Corex or Pyrex filters, was reported by Klett and Johnson to yield the allylic methyl ether 17 as the major photoproduct along with 18 and 19 (in ratios of 10 1 1). Similar reactions of triphenylallene 20 and 1,3-diphenylallene 21 also afford aUyl ethers 22,23 (5 1), and 24, respectively. In these reactions, a mechanism involving a strongly polarized planar singlet excited state is proposed on the basis of triplet sensitization experiments. 

The photochemical reactions of allenes via an electron-transfer pathway have also been reported. The triplet-sensitized reaction of tetraphenylallene 16 in the presence of xanthone was reported by Klett and Johnson to afford only vinyl ether 43. They also reported that the photochemical reaction (X, >330 nm) of triphenylallene 20 in methanol in the presence of 1,4-dicyanonaphthalene (1,4-DCN) yields vinyl ethers 44-46 via an electron-transfer pathway, together with aUyl ether 47 and alkyne 33. In this reaction, the radical cation of allene 48 is assumed to be the key intermediate. 

Mariano and co-workers also reported the photochemistry of aUenes using an electron-transfer sensitizer.Irradiation of allenes 12,49, and 50 in the presence of 2-phenylpyrrohnium perchlorate affords adducts 51 and 52, 53 to 55, and 56, respectively. In these reactions, the radical cation of allene 57 and pyrrolidinyl radical 58 are assumed to be the key intermediates. Mangion and co-workers reported the photochemical reactions of allenes with cyanoarenes. For example, irradiation of 1,2,4,5-tetracyanobenzene 59 and tetramethylallene 50 in acetonitrile-methanol (3 1) through a Pyrex filter leads to 1 1 1 arene-aUene-methanol adduct 60. Similar reaction of 1,1-dimethylaUene 49 also affords adducts 61 and 62. 

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