John D. Coyle

Photocycloaddition reactions of N-methylthiophthalimide

Abstract N -Methylthiophthalimide undergoes a photochemical cycloaddition reaction with 2,3-dimethylbut-2-ene or with stilbene to give products containing a spiro-thietane system; with 1,1-diphenylethene the product isolated is a diphenylmethyleneisoindoline.

Phthalimide and Its Derivatives

Organic carbonyl compounds featured prominently in the early period of mushrooming growth in the field of organic photochemistry. Initially much attention was focused on the photoreactions of ketones and, to a lesser extent, aldehydes. Subsequently carboxylic acids and their derivatives were investigated more extensively, and reviews of their photochemistry show a wide range of interesting reactions.(1,2) Cyclic carboximides have emerged as showing a considerable variety of photochemical behavior, and many of the reactions can be put to good use in the synthesis of heterocyclic compounds. Reactions of the hydrogen abstraction/cyclization type have been reviewed by the director of the most active research group in this area,(3) and a more comprehensive review of imide photochemistry is available.(4) The purpose of this chapter is to describe the photochemical reactions of aromatic imides related to phthalimide, and to emphasize the synthetic applications of the processes. At various points in the discussion the main parallels and differences between aromatic and aliphatic imides will also be covered briefly.

A photochemical approach to protoberberine alkaloids

Abstract Photochemical cyclisation of methoxy-substituted N -(1,2,3,4-tetrahydroisoquinolin-2-ylmethyl)phthalimides and subsequent treatment of the photoproduct with aqueous acid leads to oxygenated compounds with the protoberberine skeleton.

Photochemical hydrogen abstraction and cyclisation in maleimide derivatives

Abstract N -(2-Morpholinylethyl) derivatives of maleimide, 3,4,5,6-tetrahydrophthalimide and phthalimide give rise to products with a new hexahydropyrazine ring, in contrast to the corresponding derivative of 1,2,3,6-tetrahydrophthalimide which gives an octahydrobenzazepinedione.

Photochemically induced ring-opening in prolyl peptides

Abstract Irradiation of prolylglycine in neutral, aqueous solution results in decarboxylative ring-opening to 5-amino-N-hydroxymethylpentanamide.

Photoinduced electron transfer in aliphatic peptides

Product analysis in the photolysis of triglycine in neutral aqueous solution suggests that the initial intramolecular electron transfer from the carboxylate to the peptide group, shown to lead to efficient (ϕ 0.44 ± 0.11) photodegradation for glycylglycine, may be followed by transfer to the second peptide group.

Photocycloaddition of N-methylthiophthalimide with alkynes

Abstract N -Methylthiophthalimide undergoes photochemical cycloaddition reactions with diphenylacetylene, hex-3-yne and bis(methylthio)acetylene to form spiro-thietes; in solution the spiro-thiete from the bis(methylthio)alkyne is in equilibrium with its ring-opened isomer.

Photochemical cycloaddition of thiocarbonyl compounds to diphenylketene and a related ketenimine

Diphenylketene undergoes photocycloaddition with N-methylthiophthalimide, N-methyldithiophthalimide or xanthene-9-thione, to give a Spiro-adduct containing a thietan-2-one ring. The photoproducts from the thioimide substrates are themselves photolabile, eliminating COS to form an alkene. Diphenyl-N-(p-tolyl)ketenimine gives analogous 2-iminothietanes on irradiation with the thioimides.

Photocycloaddition reactions of thioimides with alkynes

Photochemical reaction between N-methyl(thiophthalimide) and diphenylethyne or hex-3-yne involves selective cycloaddition at the CS bond, and yields a spiro-thiete product. A related spiro-1,2-dithiole isolated from the reaction mixture may be formed during the work-up procedure. With bis-(alkythio)ethynes, both N-methyl(thiophthalimide) and N-methyl(dithiophthalimide) form α-alkythio α,β-unsaturated dithioesters; such 1 : 1 adducts are most readily explained on the basis of initial spiro-thiete formation.

Photochemical cycloaddition reactions of N-methyl(thiophthalimide) and N-methyl(dithiophthalimide) with alkenes

Irradiation of N-methyl(thiophthalimide) with alkenes leads to reaction at the thiocarbonyl, rather than at the carbonyl, group of the thioimide. Products isolated include (2 + 2) cycloadducts (isoindole-1-spiro-2′-thietanes), a cleavage product (a 3-alkylideneisoindol-1-one) derived from such cycloadducts, or (2 + 2 + 2) cycloadducts incorporating two molecules of thioimide (1,4-dithiane-2,3-bis-spiroiso-indoles). The products are consistent with a mechanism that involves an intermediate 1,4-biradical, and they contrast markedly with those obtained from N-methylphthalimide with alkenes. N-Methyl-(dithiophthalimide) is less effective in photoreactions with alkenes, and in only one instance was a cycloadduct formed at a reasonable rate and isolated; possible reasons for this difference are discussed.