NMR study of complex triquinanes and bulleranes derived from photoisomerization of aryl‐substituted norbornan‐2‐ones

Abstract

Analysis of 'H and I3C NMR data by 2D NMR techniques was used for the structural identification of triquinanes and bulleranes considered as precursors of complex natural products such as ( +)-cerapicol. The polycyclic molecules are derived from a tandem Norrish Type I photoreaction and intramolecular arene-alkene meta photocycloaddition of aryl-substituted norbornan-2-ones.

Photochemical strategies for the construction of polycyclic molecules

“…An intramolecular meta-cycloaddition-based strategy is also quite appropriate to synthesize linear triquinanes, such as (±)-coriolin (15) (eq 3).9 Following meta (3) photocycloaddition of the substrate 12 to the photocycloadduct 13 (15%), the linearly fused triquinane skeleton of coriolin is elaborated by reduction of 13 and treatment with thiophenol, leading to preferential cleavage of one of the allylic three-membered ring bonds. The resulting triquinane 14 is subsequently converted to coriolin (15) through a series of straightforward steps.…”

“…Treatment of 52 with dilute acetic acid provoked opening of the nonallylic bond in the three-membered ring to the lactol 54 and the corresponding acetate 55 (eq 10). 15 Lactol 54 was to the recently discovered bullerane skeleton represented by (+)-cerapicol (56). 18 It is of interest that both allylic cyclopropane bonds could be cleaved selectively.17 Catalytic hydrogenation of the model compound 57 afforded the tricyclic ether 58 (51 %) via hydrogenolysis of bond b (eq 10).…”

“…Solvolysis led to the alcohol 95, from which the dimethyl analogue 96 was derived. Rearrangement gave the tricyclic ketone 97, possessing the ring system of quadrone (eq 14).20 basic medium to l-(2-cyanoethyl)-2-naphthol (101) (76%) (eq 15).22 Irradiation of 100 in benzene in the presence of mercuric oxide and iodine led to ring enlargement (102). 23 Remarkably, the photocycloaddition of 2-naphthol and methyl acrylate did not proceed, while 105 wets obtained as a mixture of endo and exo adducts (57 %) from the reaction of 2-naphthyl trimethylsilyl ether (103) and methyl acrylate (104) (eq 15).24…”

“…The triquinane (±)-coriolin (15) was synthesized via the ODPM rearrangement of 154, leading to the tricyclic diketone 155 as the key step (eq 25). 49 The versatility of the method is illustrated by the synthesis of the iridoid (±)-forsythide aglucon dimethyl ester (158).…”