Applications of Phthalimide Photochemistry to Macrocyclic Polyether, Polythioether, and Polyamide Synthesis

Abstract

Irradiation of phthalimides which contain N-linked omega-trimethylsilylmethyl-substituted polyether, polythioether, and polysulfonamide chains results in efficient production of the corresponding macrocyclic polyether, polythioether, and polysulfonamide products. These photocyclization reactions follow sequential single electron transfer (SET)-desilylation pathways. Only in the cases of phthalimides, bearing mixed ether-thioether N-substituents, do these excited-state cyclization reactions proceed with lower degrees of regioselectivity. This is a result of competitive desilylation and alpha-to-sulfur deprotonation reactions of the zwitterionic diradical intermediates formed by initial SET.

Carbon–Carbon Bond Forming Reactions via Photogenerated Intermediates

“…The desired macrocycles 207a,b were then obtained via radical recombination. 179 An intramolecular photoinduced electron transfer was also reported in the Witkop cyclization applied to the multistep synthesis of monoterpenoid indole alkaloid (−)-leuconoxine. 181 Intramolecular arylation of vinyl cations 209 in Scheme 70).…”

“…The excellent properties of the trimethylsilyl or of the carboxylate substituents as electroauxilary group (section ) have been exploited for the preparation of macrocyclic polyethers, polythioethers, and polyamides. , As illustrated in Scheme , irradiation of N -substituted phthalimides 204a , b caused an intramolecular SET reaction (see intermediates 205a,b ) that was followed by loss of the trimethylsilyl cation and protonation to form biradicals 206a , b . The desired macrocycles 207a , b were then obtained via radical recombination . An intramolecular photoinduced electron transfer was also reported in the Witkop cyclization applied to the multistep synthesis of monoterpenoid indole alkaloid (−)-leuconoxine …”

Direct and indirect single electron transfer (SET)-photochemical approaches for the preparation of novel phthalimide and naphthalimide-based lariat-type crown ethers

“…In these studies, we assumed that photoirradiation of the bis-donor-linked bis-phthalimides could result in the formation of various interconverting zwitterionic biradicals through SET from donor sites in either oxygen-containing chain to either phthalimide acceptor. Based on observations made in earlier studies that the SET process displays a distance-dependence between donor and acceptor, we anticipated that the most efficient reaction pathway would involve a SET between the closest donor and acceptor moieties rather than the more distant pairs and that this event would selectively and sequentially produce zwitterionic biradicals related to 64 and 67 [31–32 67]. Based on this reasoning, we predicted that bis-crown ethers rather than their cross bridged counterparts would be generated in photoreactions of the α-silyl ether-terminated, polyethyleneoxy-linked bis-phthalimides 56 – 59 .…”

A strategy for the preparation of cyclic polyarenes based on single electron transfer-promoted photocyclization reactions

“…Two examples of the preparatively useful SET photochemical processes involving allyl-and benzylsilanes are the photocyclization reaction of the N-allysilane containing iminium salt 22, which serves as a cornerstone of a route for the synthesis of the harringtonine alkaloid cephalotaxine (Scheme 6) [11], and the photoinduced conversion of the Nbenzyl-dihydroisoquinolinium salt 23, the key final step in a concise sequence for the synthesis of the protoberberine alkaloid stylopine (Scheme 7) [12]. In addition, the role played by desilylation of cation radicals of many other silicone-containing electron donors, including a-silyl-ethers, -thioethers, -amine, -amides andsulfonamides, in preparatively useful SET-promoted photochemical reactions has been demonstrated [13][14][15][16]. A specific example that can be used to point out the preparative potential of SET photochemical processes of this type is the photomacrocyclization reaction of the phthalimide 24, containing a polyether tethered trimethylsilyl ether group (Scheme 8) [17].…”