Shinsaku Fujita

Synthetic and structural studies of [6]-, [7]- and [10]metacyclophanes

Abstract A new preparative sequence from 2,3-polymethylene-2-cyclopentenone 5 to 2,6-polymethylenebromobenzenes 3 (n = 6, 7, 10) and 2,6-polymethylenephenyllithiums 6 has been found. The reaction of 6 with various electrophiles produces a number of new compounds to disclose the unique reactivity of the aryl C-Li moiety surrounded by the polymethylene chain. Photolysis of 3a and 3b provides transannular products 8, 10 and 11 , all arising from the proximity between the aromatic bromine and the aliphatic hydrogen intraannularly opposed to be removed as HBr. Spectrometric study gives quantitative data of the dependence of the molecular geometry upon the chain length and the aromatic substituents. The energy barriers ΔG c ≠ of the conformational flipping are 17·4 kcal/mol (T c 76·5°) for [6]metacyclophane ( 7a ), 11·5 kcal/mol (T c −28°) for [7]metacyclophane ( 7b ), ·8 kcal/mol for [10]metacyclophane ( 7c ). The lower-energy process of the aliphatic chain in [6]metacyclophane derivatives is the pseudorotation with substituent-dependent barrier ΔG c ≠ 11·1 kcal/mol (T c −31·5°) for 7a , 12·4 kcal/mol (T c −4·5°) for 3a and 12·7 kcal/mol (T c 1·0°) for 12a . The rather large rotational barrier is attributed to the compressed structure of each system. The benzene ring distortion of the cyclophanes is deduced from the bathochromic shift of the B-band and the diamagnetic shift of the benzene proton signals in the PMR.

Photochemical reaction of ethyl azidoformate with cyclic ethers and acetals

Abstract Irradiation of ethyl azidoformate dissolved in cyclic ethers (IIIA-VA) and acetals (VIA-VIIIA) yields insertion products (IIIB-VIIIB) of carboethoxynitrenes (IIS and IIT). The attack of the nitrenes occurs exclusively at the Cue5f8H bond adjacent to the ether oxygen or adjoining acetal oxygens to produce a single insertion product in each case. Byproducts are urethane (IX) and the dimerization product (X) of amino radicals (XI). The effects of acetophenone as a sensitizer and of methylene chloride as a diluent have been examined and discussed. Reduction of IIIB and IVB with LAH produces 4-methylaminobutan-1-ol and 5-methylaminopentan-1-ol in 62 and 83% yields, respectively.

Reaction of N-alkoxycarbonylaziridines with nitriles

Abstract The acid catalysed reaction of acetonitrile or benzonitrile with N-alkoxycarbonylaziridines, 1a and 1b yields the corresponding 1-alkoxycarbonyl-2-imidazolines, 2ax , 2ay , and 2bx . The imidazolines obtained by the reaction of N-ethoxycarbonyl-2,3-tetramethyleneaziridine ( 1c ) with acetonitrileor benzonitrile are labile and are readily hydrolysed to trans -cyclohexane-1,2-diamine derivatives ( 3cx or 3cy ). The nitrile-addition supposedly proceeds S N 2 type Cue5f8N bond cleavage and Cue5f8N bond formation.

The photochemistry of 1,2,3-triphenylaziridine

Abstract Photochemical behaviour of 1,2,3-triphenylaziridine has been investigated. Irradiation in alcoholic solvents induces a novel type of alcoholytic cleavage of the aziridine ring to give benzaldehyde acetals and N-benzylaniline. Competitively, fragmentation occurs to give rise to benzalaniline and phenylcarbene, the latter being trapped with alcohols as alkyl benzyl ethers. Photolysis in cyclohexene affords a 1,3-cycloaddition product, 1,2,3-triphenyloctahydroisoindole as a mixture of two stereoisomers.

Photochemical addition of protic solvents to 1-phenylcycloalkenes

Abstract Direct photolysis of 6–8-membered 1-phenylcycloalkenes (1a–1c) dissolved in acetic or propionic acid gives mainly the corresponding esters (2), which are also obtained in the acetophenone-sensitized reactions. Minor products in the direct photolysis of 1a and 1b are hydrogenation (3) and alkylation products (4), while 8-membered 1c yields 1-phenylbicyclo[5.1.0]octane (5) on UV irradiation. Compounds 3 and 4 are explained as the secondary photoproducts from 2. Possible species affording 2 are discussed.