Hydrocarbon Activation. Synthesis of β-Cycloalkyl (Di)nitriles through Photosensitized Conjugate Radical Addition

Abstract

Photoinduced hydrogen abstraction from aliphatic cyclic hydrocarbons (C(5) to C(7), C(12), as well as adamantane) by triplet aromatic ketones in the presence of alpha,beta-unsaturated (di)nitriles offers a straightforward entry to the corresponding alkylated (di)nitriles via the alkyl radicals. Yields are moderate to good depending on the olefins structure (substitution in beta slows down the addition to mononitriles, but with alpha,alpha-dinitriles electronic activation allows efficient alkylation also of beta,beta-disubstituted substrates). A tandem alkylation-cyclization process has been obtained with (1-methylpent-4-enylidene)malononitrile.

Polyoxotungstate Photoinduced Alkylation of Electrophilic Alkenes by Cycloalkanes

“…A single product was obtained in this case and recognized as the 3-(w-alkenyl)-3-cyclohexylhept-6-enecarbonitrile (9). On the contrary, cyclized dinitrile 10 that we had previously obtained through radical addition onto CMHN under different conditions (see Scheme 2) [14] was not formed in the present case.…”

“…[24] The electrophilic alkenes IPMN, IPCA [25] and CMHN [14] were prepared as previously reported. The other materials and the solvents were of commercial origin.…”

“…[14] Hexylcyclohexane was recognized by comparison of the GC/MS spectrum with literature data, [26] bicyclohexyl and cyclohexylmethylketone by comparison of the GC/MS spectrum with that of authentic samples. Steady state measurements: Solutions (2 mL) of 0.002 m TBADT in MeCN containing the appropriate additives in 1 cm optical path spectrophotometric couvettes were degassed by five freeze-degas-thaw cycles (to 10 À6 Torr).…”

“…Further support to the mechanism comes from the fact that when using CMHN as the trap, no cyclization takes place, while this is the main process (cyclized 10 vs open chain 9 3 to 1) [14] when the cyclohexyl radical is generated by an alternative method, for example hydrogen abstraction from cyclohexane by triplet benzophenone. Under the present conditions, on the contrary, the 5-hexenyl radical 15 is reduced by H + W 10 O 32 5À accumulated to a significant concentration to give anion 16, so that cyclization is completely inhibited (Scheme 2).…”

The photomediated reaction of alkynes with cycloalkanes

“…Most usefully and because of their nucleophilic properties, 17 they would be expected to react with molecules containing electron deficient carbon-carbon multiple bonds (Scheme 1). This approach has been used in the reaction of enones with 1,3-dioxolanes, 18 the reaction of enals with dioxolanes and alcohols, 19 and the functionalisation of cycloalkanes with alkenyl nitriles 20 and ketene dithioacetal S,Sdioxides. 21 The mechanistic framework for the process suggests that the use of "catalytic" quantities of the carbonyl compound functioning as the photomediator should be sufficient.…”