Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

Abstract

SummaryNovel cis/trans-4- and cis/trans-5-(2-vinylstyryl)oxazoles have been synthesized by Wittig reactions from the diphosphonium salt of α,α’-o-xylene dibromide, formaldehyde and 4- and 5-oxazolecarbaldehydes, respectively. In contrast, trans-5-(2-vinylstyryl)oxazole has been synthesized by the van Leusen reaction from trans-3-(2-vinylphenyl)acrylaldehyde which is prepared from o-vinylbenzaldehyde and (formylmethylene)triphenylphosphorane. The 4- and 5-(2-vinylstyryl)oxazoles afford, by photochemical intramolecular cycloaddition, diverse fused oxazoline-benzobicyclo[3.2.1]octadienes, which are identified and characterized by spectroscopic methods. The photoproducts formed are relatively unstable and spontaneously or on silica gel undergo oxazoline ring opening followed by formation of formiato- or formamido-benzobicyclo[3.2.1]octenone derivatives. On irradiation of 4-(2-vinylstyryl)oxazole small quantities of electrocyclization product, 4-(1,2-dihydronaphthalen-2-yl)oxazole, are isolated and spectroscopically characterized.

Domino Transformations of Ene/Yne Tethered Salicylaldehyde Derivatives: Pluripotent Platforms for the Construction of High sp3 Content and Privileged Architectures

“…Among others are multi‐component reactions, cycloaddition, cyclocondensation, and photocatalyzed additions. These polyfunctionalized aromatic aldehydes/ketones suitably poised with ene/yne systems in the ortho position can be easily constructed from simple and commercially available raw materials like salicylaldehydes, 2‐bromobenzaldehydes, 2‐hydroxyacetophenones, 2‐bromostyrenes, etc –. Furthermore, the carbonyl group resident on these substrates can be converted to key branching derivatives like imines, oximes, nitrones, and nitroolefins through facile reaction sequences.…”

Formation of Polycyclic Skeletons by Photochemical Transformations of Pyridyl‐ and Thienylbutadiene Derivatives

“…[2] When properly functionalized, bicyclo[3.2.1]octanes have proved to be useful reactive intermediates in stereoselective transformations. [5] During our long-standing studies in photochemical intramolecular cycloaddition reactions of various -heteroaryl-o-divinylbenzenes such as furans, [6][7][8] thiophenes, [8][9][10] pyrroles, [11,12] sydnones, [13][14][15] and most recently oxazoles, [16][17][18] routes were obtained for a whole library of polycyclic compounds that include a vast number of structures with the benzobicyclo[3.2.1]octadiene moiety (A-D) (Scheme 1). [3,4] The benzobicyclo[3.2.1]octadiene skeleton can thus be even more useful, as it can easily be transformed by adding various functional groups to the isolated double bond.…”

“…For the first time, a study of efficiency was conducted where the efficiency of intramolecular cycloaddition of these heterocyclic butadiene derivatives was investigated by simultaneous use of ferrioxalate and valerophenone actinometers. From vast previous studies of the excited state behavior conducted on stilbene moieties, [7][8][9][10][11][12][13][14][15][16][17][18] it was expected that butadiene derivatives would give, by intramolecular photocycloaddition, a new line of polycyclic products. [19] Derivatives that have been investigated so far have been those with phenyl and 2-furyl substituents (Scheme 2).…”

“…For the first time, a study of efficiency was conducted where the efficiency of intramolecular cycloaddition of these heterocyclic butadiene derivatives was investigated by simultaneous use of ferrioxalate and valerophenone actinometers. moiety with an isolated double bond (C), which can undergo further transformations by addition, or, as is the case with the 5-oxazole derivative, the oxazole opens spontaneously to give the formamide product D. [17] The natural continuation of investigations in this direction led to studies of o-vinylphenyl-substituted butadienes. [19] Derivatives that have been investigated so far have been those with phenyl and 2-furyl substituents (Scheme 2).…”

“…[19] Derivatives that have been investigated so far have been those with phenyl and 2-furyl substituents (Scheme 2). From vast previous studies of the excited state behavior conducted on stilbene moieties, [7][8][9][10][11][12][13][14][15][16][17][18] it was expected that butadiene derivatives would give, by intramolecular photocycloaddition, a new line of polycyclic products. Desired derivatives with the benzobicyclo[3.2.1]octadiene skeleton (G) as well as polycyclic products H were synthesized, purified, and described (Scheme 2).…”