Benzo xanthene

The acid-catalyzed reaction of salicylaldehydes with 2-tetralone 168 affords 12//-bcnzo[ ]xanthcncs 169. The reaction proceeds via an initial condensation of the aromatic aldehyde with the activated methylene group to form the intermediate 170. The extended enolate of the intermediate 170 undergoes electrocyclization, dehydration, and rearomatization to afford 12/7-benzo[ ]xanthenes (Scheme 54) <2004TL8999>. 

As shown in Equation (132), dihydrofurans having a 3-acetyl group underwent benzannulation via photoinduced cleavage of the dihydrofuran ring to give naphthalene products <2001TL3351>. Helicene-type compounds and benzo[/(/]xanthenes were also produced by this method <2005TL7303>. 

Studies in the laboratory of Tanaka toward the synthesis of bikaverin 20, a fungal metabolite with a benzo-xanthen skeleton, led to the discovery of an elegant method to form ring C. Upon treatment with aqueous oxalic acid, benzopyranone 16 was directly transformed into xanthone 17, which could be potentially elaborated intro bikaverin 20. The unexpected formation of intermediate 17 could be explained by the following sequence hydrolysis... 

I)ioxy-9.metliyl.9-propyl-3.4 5.6-di> benzo-xanthen 17 II209. 

Fluoren.carbonsanie.(9).anhydrid 9, 691. a.(Z.I>iphenvl.a. a -dii9ienylen.bematein> 8 ure-anhydrid 17, 561. 9.10-I>ipkenyl-9.10-dihydTo-phenanthreii dicarbone6uie-(9.10)-anhy d 17 H 520. 9-[3.4-Hethylendiozy-phenyl]-l. 2 7.8-di benzo-xanthen 19, MO. 

Benzo[ifc,/]xanthenes result from the chromium-mediated benzannulation of the carbene complex (20) <96CC895>, whilst the photooxidative cyclisation of ( )-2-styrylchromones (21) leads to benzo[a]xanthones <96HCM251>. 

Fluoran (1) is the commonly used name for the spiro [isobenzofuran- 1,9 -xanthen]-3-one. Benzo[a]fluoran (2) has the benzene ring fused to the 1-and 2-positions of the xanthene moiety. Fusion at the 3- and 4-positions gives benzo[c]fluoran (3). Numbering of the atoms is employed as shown in 1-3. 

Whitaker JE, Haugland RP, Prendergast FG (1991) Spectral and photophysical studies of benzo[c]xanthenes dyes dual emission pH sensors. Anal Biochem 194 330-344... 

SNARF and SNAFL indicators are benzo[c]xanthene dyes that can be described as semi-naphthofluoresceins and semi-naphthorhodafluors, respectively, depending on whether the benzo[c]xanthene ring is substituted at the 10-position with oxygen or with nitrogen, respectively (Whitaker et al., 1991). These indicators, whose p K l values are in the physiological range, exhibit distinct emission bands for the pro-tonated and deprotonated forms so that emission ratio measurements are possible. In SNAFL, the acidic form is more fluorescent, whereas in SNARF, the basic form is more fluorescent. 

Whitaker J. E., Haugland R. P. and Prendergast F. G. (1991) Spectral and Photophysical Studies of Benzo[c]xanthene Dyes Dual Emission pH Sensors, Anal. Biochem. 194, 330—44. 

Another mechanism of chiral amplification that extends over an even larger scale has been reported by Huck et al. [119] The molecule 12-(9 H-thioxantbene-9 -yli-dene-12H-benzo[a]xanthene (Fig. 11.6), which has no chiral center, nevertheless exists, like the helicenes, in two chiral forms defined by their enantiomeric configurations. Consistent with the discussion in Section 11.2.3, a small net handedness (ca. 0.7 %) could be induced in racemic solutions of this molecule by use of ultraviolet CPL. However, introducing 20 wt% of this molecule, which contained a 1.5% chiral excess of one roto-enantiomer, into a nematic phase of liquid crystals produced macroscopic (100 pm) regions of a chiral cholesteric liquid crystal phase. The... 

Fig. 11.6 Conversion of one enantiomer to the other by CPL. The molecule 12-(9 H-thioxan-thene-9 -ylidene)-l 2H-benzo[a]xanthene exists in one of two chiral forms that can be intercon-...

Wang RZ, Zhang LF, Cui ZS (2009) Iodine-catalyzed synthesis of 12-aryl-8,9,10,12-tetra-hydro-benzo a xanthen-ll-one derivatives via multicomponent reaction. Synth Commun 39 2101-2107... 

All of the compounds discussed are based on three molecules 2/f-pyran (1), 4//-pyran (2) and the pyrylium cation (3). Names which have been used for the benzologue (4) of 2//-pyran include 2H- 1-benzopyran, benzo-a-pyran, chrom-3-ene and 2//-chromene. A similar situation exists for the corresponding derivative (5) of 4/f-pyran. The unambiguous and simplest name chromene is used in the present work. The benzologue (6) of pyrylium is known both as benzopyrylium and chromylium the former name is preferred here. Higher benzologues are referred to as naphthopyrans, such as 2H-naphtho[ 1,2-6 jpyran (7), but the names xanthene and xanthylium are used for (8) and (9). 

Six-membered unsaturated oxygen heterocyclic compounds are based on three molecules 2/7-pyran 1,4/7-pyran 2, and the pyrylium ion 3. Based on this, the benzo analog of 2/7-pyran is named 277-1-benzopyran (commonly 2H-chromene) and the benzo analog of 477-pyran is called 4/7-1-benzopyran (commonly 477-chromene). The benzo analog of 3 is known as 1-benzopyrylium 6 (sometimes chromylium). Related naphthyl analogs are exemplified by 2/7-naphtho[l,2,A]pyran 7, the xanthylium ion 8, and xanthene 9. 

Benzo[a] and benzo[c] xanthene and dibenzo[a,c]xanthene have been synthesised by the Pd-catalysed cyclisation of aromatic 2-(arylmethyl)phenol triflate esters through S-0 bond cleavage <02T5927>. 

Benzo[fe]xanthene-6,l 1,12-triones are readily available through the photo-induced 1,4-acylation of naphthoquinone with 2-hydroxybenzaldehydes followed by oxidation <02H(57)1915>. Chromone-3-carboxaldehyde reacts with o-benzoquinodimethane in a DA reaction with concomitant deformylation to give a diastereoisomeric mixture of tetrahydrobenzo[fc]xanthones oxidation can be accomplished with DMSO/I2 <02T105>. 

TCBTs are relatively persistent and non-flammable (and therefore useful in hydraulic oils). Pyrolysis in a closed system for two days in the presence of hydrogen peroxide at 300 °C produced as main components chlorinated benzo-phenones, fluorenes, fluorenones, xanthenes, and xanthones. Polychlorodiben-zofurans (PCDF) and polychlorodibenzo-p-dioxins (PCDD) were formed in much lower concentrations than from PCB product Pyralene T1 under identical conditions [84]. In pyrolysis at 450-700 °C with excess oxygen TCBTs produce more PCDFs and PCDDs. In parallel with the behavior of PCBs, PCDFs are formed in significantly higher amounts than PCDDs from PCBTs [86],... 

H-benzo[a]xanthen-12-ones (231). Over the years Heller and... 

R - H Essigsiure) 3-Methyl-2-[2-( 5,6,9 JO-tetrahydro-(benZo[e -1 H-xanthen -11 -yl)-ethenyl 1 J-benzothiazohum-perchlorat666... 

Methyl-2- 2-(5,6,9,10-tetrahydro-(benzo[el-)H-xanthen)-ll-yl)-ethenyl - 995 3-(2,2,2-Trifluor-ethyl)- -trifluormethansulfonat 942... 

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