Lamps photochemical syntheses with

Aoyama et al. in relation to their studies on photochemical synthesis of (3-lactams [91] reported the synthesis of 4-spirocyclopropylazetidin-2-one [92] via photocycloaddition of 4-thioxoazetidin-2-one to alkenes followed by subsequent desulfurization. A solution of 1-isopropyl-3-phenyl-4-thioxoazetidin-2-one 70 and 1,1-diphenylethylene in benzene on irradiation with a high pressure mercury lamp afforded a [2 + 2] adduct 72 (R = Ph), in 67% yield which, on desulfurization with Raney-nickel [93] in anhydrous ethanol gave two isomeric... 

N-Debenzylation. N-Benzylpyrrolidine and a little 9,10-dicyanoanthracene as electron acceptor in 7 3 acetonitrile/water irradiated for 6-10 h in a Pyrex tube with a 450 W Hanovia lamp (405 nm) fitted with a CuS04 NH3 soln. filter - pyrrolidine, Y 90%. The method is not applicable to deprotection of a-aminoacids. F.e.s. G. Pandey, K.S. Rani, Tetrahedron Letters 29, 4157-8 (1988) N-demethylation with N,N -dimethyl-2,7-diazapyrenium fluoroborate as electron acceptor s. J. Santamaria et al., ibid. 30, 2927-8 (1989) review of photo-induced electron transfer s, J, Mattay, Synthesis 1989, 233-52 review of single electron transfer (SET) s. E.C. Ashby, Acc. Chem. Res. 21, 414-21 (1988) review of new developments in photochemical synthesis s. M. Demuth, G. Mikhail, Synthesis 1989, 145-62. 

An improved synthesis of 3,4-dihydro-2,l-benzothiazine 2,2-dioxide was reported by Togo and co-workers using photochemical conditions . Treatment of A-alkyl 2-(aryl)ethanesulfonamides 18 with (diacetoxyiodo)arenes under irradiation with a tungsten lamp at 20-30 °C afforded 2,1-benzothiazines 19 and 20. Chemical yields and selectivities were dependent upon the choice of solvents and the reactant s substituents 18 (Table 1). When THF and EtOH were used as solvents, the reactions failed to give the cyclized products, since their a-hydrogen was abstracted by the intermediate sulfonamidyl radical. Compound 20 was obtained as a major product when 1,2-dichloroethane was employed as a solvent. In contrast, in the case of EtOAc as solvent, compound 19 was obtained as the major product. 

Eaton and co-workers also reported the synthesis of 1,3,5-trinitrocubane and 1,3,5,7-tetranitrocubane (39) ° The required tri- and tetra-substituted cubane precursors were initially prepared via stepwise substitution of the cubane core using amide functionality to permit ort/jo-lithiation of adjacent positions. The synthesis of precursors like cubane-1,3,5,7-tetracarboxylic acid was long and inefficient by this method and required the synthesis of toxic organomercury intermediates. Bashir-Hashemi reported an ingenious route to cubane-1,3,5,7-tetracarboxylic acid chloride (35) involving photochemical chlorocarbonylation of cubane carboxylic acid chloride (34) with a mercury lamp and excess oxalyl chloride. Under optimum conditions this reaction is reported to give a 70 8 22 isomeric mixture of 35 36 37... 

The thermal Diels-Alder reaction ([4 + 2] cycloaddition) is widespread in the synthesis of fullerene derivatives. In contrast, only a few examples of the photochemical Diels-Alder reaction in solution or in the solid state are known. The first example is described by Tomioka and coworkers [249], Irradiation of ketone 73 and C6o at 10°C with a high pressure mercury lamp through a Pyrex filter led to the formation of 61-hydroxy-61-phenyl-l,9-(methano[l,2]benzenomethano) fullerene 75 (Scheme 29). This compound is unusually unstable and yields the monoalky 1-1,2-dihydrofullerene 76 either by silica gel chromatography or upon heating. 

The stereoselective total synthesis of tt)-campherenone was accomplished by T. Uyehara and co-workers based on a photochemical Wolff rearrangement. The bicyclic ketone was treated with 2,4,6-triisopropylbenzenesulfonyl azide (trisyl azide) under homogeneous basic conditions and the a-diazo ketone was obtained in excellent yield. The photochemical rearrangement of the diazo ketone was conducted in a THF-water mixture using a high-pressure 100 W mercury lamp. The ring-contracted acid was isolated as a 4 1 mixture of endo and exo products. 

Diazencs with a variety of substituents have been investigated for the synthesis of either linearly fused or bridged cycloadducts (Table 2). Typical experimental conditions are either refluxing the diazene in a solvent (acetonitrile, THF, or methanol) or irradiation with UV light (high-pressure mercury arc lamp and Pyrex filter). Determination of the activation parameters revealed that the thermal, as well as the photochemical, deazetation proceed via a common 1,3-diyl intermediate27. 

Photochemical CDC reactions were first carried out for the synthesis of [7]circulene hy Yamamoto, Kai, and Kasai in 1988 (Scheme 8.62). Cyclo-phadiene (125) was irradiated with a high-pressure Hg lamp in the presence of a small amount of iodine to furnish the dehydrohexahelicene 126 in 42% yield, which was successfully converted to [7]circulene. 

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