5,6‐Didehydro‐11,12‐dihydrodibenzo[a,e]‐cyclooctene

Abstract

the diazo compound to acetylenedicarboxylate, also yields spirocyclopropenes (in analogy to the findings of Ege [41) or their subsequent reaction products. We found, however, that irradiation of ( l a ) -( l c ) in benzene leads to benzocyclopropenes (Za)-(Zc). hv R3 H5C6 COOCH, I I I I 175 85 187 86 158 30The NMR and IR spectra of (2a)-(2c) show few signals and bands respectively, and demonstrate the high degree of symmetry of the molecules. Thus the two methoxycarbonyl groups appear as a singlet at 6 = 3.81 ppm (6H) in the NMR spectrum of (Za), and a multiplet due to the aromatic protons is observed at 6.8-7.4 ppm (20 H) (in CDC13 with TMS as internal reference). Catalytic hydrogenation of (Zb) in acetic ester with PtOz as catalyst affords the terphenylylmalonic ester (3b) [6 = 3.37 ppm (6H, s); 4.98 ppm (1 H, s); 7.2-7.8 (12H, m); 7.94 ( l H , d)]. This finding is in accord with observations by Vogel et al. [51, who obtained benzene derivatives in addition to cycloheptanes on catalytic hydrogenation of benzocyclopropene. C6H5 ,COOR Hydrolysis of the diesters (Za) proceeds without rearrangement to give the dicarboxylic acid (#a), which can be esterified by treatment with diazomethane to (2a). In quinoline, (4a) undergoes rearrangement, with decarboxylation, to tetraphenylcoumaranone (5a) (IR: v(C0) 1820 cm-1). If (2a)-(2c) are heated above their melting points, they isomerize to the substituted benzofurans (6a)-(6c) (cf. ref. [61). All these reactions are typical of benzocyclopropenes. Dimethyl 2,3,4,5-tetraphenyIbenzocyclopropene-I,I-dicarboxylate (2a) and methyl 2-methoxy-4,5,6,7-tetraphenyIbenzo-[b] furan-3-carboxyIate (6a) Compound (la) (1.40 g, 2.6 mmole) is dissolved in anhydrous benzene (150 ml). After passage of N2 for 15 min, the solution is irradiated for 90 min (Philips HPK 125 W, h 2 280 nm, Pyrex filter). Removal of the solvent leaves a reddish oil which is taken up in methylene chloride and treated with methanol, whereupon colorless needles of (2a) (m.p. 175 "C, yield 1.13 g, 85 %) are precipitated [v(CO) = 1755 cm-1; M+= 510, m/e = 479 (M-OCHd, 451 (M-COOCH3)][71.If (2a) (1.00 g) is heated at a temperature slightly above its melting point the melt soon solidifies. Colorless needles of (6a) (m.p. 227 "C, yield 0.92 g, 92%) are precipitated from a methylene chloride/methanolsolution ofthesolidified melt 171.

Strain‐Promoted Alkyne–Azide Cycloadditions (SPAAC) Reveal New Features of Glycoconjugate Biosynthesis

“…[12] The latter compound was reduced with NaBH 4 (→ 6 ), brominated with bromine in chloroform (→ 7 ), and then treated with LDA in THF [13] to give target compound 3 in a yield of 57%. In an alternative approach, intermediate 6 was obtained by base-mediated ring opening of Kagan’s ether, which was prepared by a double Friedel-Crafts alkylation phenylacetaldehyde.…”

Bioorthogonal Fluorescent Labeling of Functional G‐Protein‐Coupled Receptors

“…[31a] In order to overcome problems such as low reactivity, poor reagent stability, and difficult synthetic pathways of the earlier cyclooctynes for bioconjugations, Boons and colleagues introduced dibenzocyclooctyne derivatives for bioconjugations by SpAAC [36] based on a 1969 report on the spontaneous reaction of dibenzocyclooctyne with phenyl azide. [37] Despite the reports of degradation of the cyclooctyne BARAC in presence of glutathione, [38] it was generally believed that SpAAC involving the cyclooctynes results in low background labeling. [31c] In a recent study, three cyclooctynes, DIBO, BCN, and DIBAC were used to evaluate azide-independent labeling of proteins, demonstrating that all of these reagents exhibited undesirable reactivities to varying extents, by a radical-based thiol-yne addition mechanism that modifies cysteine residues in proteins.…”

Click Functionalization of a Dibenzocyclooctyne‐Containing Conjugated Polyimine

“…[34] Thes trained cyclooctyne within the dibromo-DIBAC structure permitted rapid transformation of the alkynes into conjugated triazoles,t hereby altering their electronic and physical properties.U nfortunately,w ew ere unable to introduce the cyclooctyne moiety into the backbone of ap olymer because the metal catalysts used in most cross-coupling polymerizations (Ni, Pd, Cu) rapidly underwent cycloaddition reactions with the strained alkyne of the monomer,r ather than the desired oxidative addition at the carbon-halogen bond. [49] Thestructurally most simple parent structure,dibenzocyclooctyne (DIBO), [50] is ideal as am onomer for conjugated polymer synthesis because it has ar elatively planar, symmetrical structure. [44,45] Many of these methods have been demonstrated to yield high-molecular-weight polymers,a nd aw ide variety of structural diversity has been explored.…”

“…[35][36][37] This led us to explore polymerization methods that do not involve the use of transition-metal catalysts,i ncluding reactions such as the Wittig,H orner-Wadsworth-Emmons, [38][39][40] Aza-Wittig, [41,42] and Knoevenagel condensation, [43] as well as Schiff-base formation. [50][51][52][53][54] In our hands,t he synthetic approach based on aWittig-PrØvost homologation sequence was found to be compatible with initial introduction of aryl halides (in this case,i odides), which could subsequently be converted into the required amines in the target monomer 6 (DIBO-(NH 2 ) 2 ). Amongst these,S chiff-base formation offers several advantages:i thas been well-explored, [46][47][48] can produce high-molecular-weight polymers,a nd the installation of amine groups is straightforward to achieve by using Buchwald-Hartwig chemistry.…”

“…Amongst these,S chiff-base formation offers several advantages:i thas been well-explored, [46][47][48] can produce high-molecular-weight polymers,a nd the installation of amine groups is straightforward to achieve by using Buchwald-Hartwig chemistry. [49] Thestructurally most simple parent structure,dibenzocyclooctyne (DIBO), [50] is ideal as am onomer for conjugated polymer synthesis because it has ar elatively planar, symmetrical structure. [50][51][52][53][54] In our hands,t he synthetic approach based on aWittig-PrØvost homologation sequence was found to be compatible with initial introduction of aryl halides (in this case,i odides), which could subsequently be converted into the required amines in the target monomer 6 (DIBO-(NH 2 ) 2 ).…”