Chromene derivatives

Reaction of nitro-2f/-chromene derivatives 134 with 135 in methanol at room temperature afforded a mixture of the Z-isomer 136 and tricyclic compound 137, which could be formed by denitrocyclization reaction of the corresponding primarily formed E-isomer and the following dehydrogenation (Eq. 15). The structural identification was based on the MS and H-NMR, however, it is not sufficiently documented and similar examples are not known (91IJC(B)297). 

The reaction of tetrachlorobenzyne with cinnamaldehyde gave 5,6,7,8-tetrachloroflavene 124, X = C1) 155>. Similarly reactions with aliphatic a,(3-unsaturated aldehydes gave 2 /f-chromen derivatives (125) 156,157). 

There are now many examples of the industrial use of manganese(lll) salen catalyzed asymmetric epoxidations. For example, the as5mmetric epoxidation of a chromene derivative was central to the S5mthesis of the potassium channel activator BRL 55834 (Figure 11.5). ... 

Various other chromene derivatives 176a-d could be epoxidized with Katsuki s Mn-salen catalyst 173d using either H2O2 or TMS2O2 as oxidant. With this catalytic system several axial ligands (none, 7V-methylimidazole, pyridine TV-oxide) and additives (none. 

NH4CIO4, NELtPFe) have been tested and the best results were obtained in acetonitrile as solvent in the presence of Ai-methylimidazole using H2O2 as terminal oxidant (Scheme 92). Under these conditions chromene derivatives could be converted into the corresponding epoxides 177 in yields between 55 and 98% and ee values of 88-95%. 

SCHEME 92. Mn-catalyzed enantioselective epoxidation of chromene derivatives using H2O2... 

Wattanapiromsakul, C. and Waterman, P.G., Flavanone, triterpene and chromene derivatives from the stems of Paramignya griffithii. Phytochemistry, 55, 269, 2000. 

Very recently, Fujii and Ohno developed a route for the synthesis of dihydroquinoline and chromene derivatives under mild reaction conditions. Hydroarylation leads to a highly selective formation of six-membered rings, depending on the carbon (terminal or central allenic) that reacts with the aryl moiety [50]. 

The formation of 3-bromo-2-phenylchroman from the propanol derivative (246) is of interest because it forms part of the sequence utilized in the conversion of 4//-chromene into a 2//-chromene derivative (Scheme 62) (71S149). 

The six-membered ring 85 is obtained from the allylamine 84 [31]. The sulfur-containing ring 87 was obtained from 86 using the Mo catalyst. The Ru catalyst is not active for this reaction [32]. The (S, f )-chromene derivative 89 was obtained in 97% yield by the Mo-catalysed intramolecular metathesis of (S,f )-cycloheptenyl styrenyl ether 88 under an atmosphere of ethylene. In the absence of ethylene, 89 and its dimer were obtained. The enantioselective total synthesis of (.S, / ,/ , / )-ncbivoIoI (90) has been carried out from 89 [33]. No cyclization of the cyclopentene 91 was observed, because the highly strained cyclobutane intermediate 92 is difficult to form. 

Regardless of the mechanism, the chiral (salen)Mn-mediated epoxidation of unfunctionalized alkenes represents a methodology with constantly expanding generality. Very mild and neutral conditions can be achieved, as illustrated by Adam s epoxidation of chromene derivatives 12 using Jacobsen-type catalysts and dimethyldioxirane as a terminal oxidant [95TL3669]. Similarly, periodates can be employed as the stoichiometric oxidant in the epoxidation of cis- and tram-olefins [95TL319],... 

The photochromic properties of 2/7-chromene derivatives has generated much interest in recent years. Under UV irradiation these molecules can undergo reversible electrocyclic opening of the pyran ring to afford colored ortho-quinone methides <2005T11730, 2005T1681>. 

Hydroxybenzaldehydes and 2-hydroxy-l-naphthaldehydes react under Baylis-Hillman conditions with various activated alkenes to yield 3-substituted 2//-chromene derivatives (Equation 35) <2002J(P1)1318>. 2-Hydroxybenzaldehyde also reacts with acrylic acid and acrylic esters under Baylis-Hillman conditions to afford 3-carboxylatc-2//-chromenes in high yield <2001SC1233>. 

The diyne 66 undergoes an intramolecular dehydro Diels-Alder reaction in toluene under reflux to afford naphtho[2,3-c]chromene derivatives in reasonable yield (Scheme 20). The reaction is presumed to proceed via a [4+2]-cycloaddition of the alkyne to the aryl alkyne group to form the cyclic allene intermediate 67, which then isomerizes to the aromatic product <2003SL1524>. 

The 2-allyl-277-chromene derivative 73 is synthesized from 477-chromen l-one by in situ formation of the 4-silyloxy-benzopyrylium salt 74 followed by reaction with allyltri- -butyltin (Scheme 25) <2001T1005>. 

Quaternary ammonium hydroxides anchored on MCM-41 provide stronger base catalysts than amine analogues11731 and were able to catalyse the same reaction as previously reported namely for the intermolecular Michael reaction leading to flavanone.[181] Moreover, this catalyst induced the successive intramolecular olefinic attack of the phenolic group from the Knoevenagel condensation product of salicylaldehyde and diethyl glutaconate (Scheme 9.6). This fast cyclization leads to chromene derivatives (1) from which subsequent conversions induced by proton abstraction from the alpha position of the ester function gives coumarin... 

Instead of attachment of the complex by its aromatic rings, the asymmetric diamine moiety was used as an anchoring point (93). With the pyrrolidine-salen type complex 7e, high yields and ee values were observed in the epox-idation of chromene derivatives ... 

A somewhat different approach to catalyst separation has been devised by engineering the chiral salen catalyst to have built-in phase-transfer capability, as exemplified by the Mn(III) complex 10 <02TL2665>. Thus, enantioselective epoxidation of chromene derivatives (e.g. 11) in the presence of 2 mol% catalyst 10 under phase transfer conditions (methylene chloride and aqueous sodium hypochlorite) proceeded in excellent yield and very good ee s. The catalyst loading could be reduced to about 0.4% with only marginal loss of efficiency. 

A-Aminophthalimide (118) can also be added to olefins in an asymmetric fashion. Thus, reaction of A -enoyl oxazolidinone 122 with 118 and lead tetraacetate in the presence of the camphor-derived chiral ligand 120 provides aziridine 123 in 83% yield and with 95% ee <020L1107>. Other useful chiral ligands include imine 121, derived from the condensation of 2,2 -diamino-6,6 -dimethylbiphenyl with 2,6-dichlorobenzaldehyde. The corresponding monometallic Cu(I) complex was found to be very efficient in chiral nitrogen transfer onto chromene derivative 124 using (Ar-(p-toluenesulfonyl)imino)phenyliodinane (PhI=NTs) to provide aziridine 125 in 87% yield and 99% ee <02JOC3450>. 

The cyclohexadienone 10 undergoes an intramolecular asymmetric Heck reaction in the presence of a chiral monodentate phosphoramidate ligand to give the benzo[c]chromene derivative 11 with excellent enantioselectivity and conversion <02JA184>. 

The boron-Mannich condensation was assisted by a hydroxy group adjacent to the aldehyde moiety. The products derived from salicylaldehydes and vinylboronic acids underwent cyclization to 2H-chromene derivatives with elimination of the amine upon heating (Equation (119)).566... 

M. Uchida and M. Irie, Photochromic chromene derivatives with a thiophene moiety, Chem. Lett., 1992, 2257-2260. 

Consequently, we anticipated that to overcome these problems it might be important to incorporate moieties in the precocene structure to alter the transport properties of the natural compounds. For this aim, we synthesized crown ether precocenes VII (11), in which C-6 and C-7 of the chromene skeleton were incorporated into a 15-crown-5 or 18-crown-6 ether ring. We also prepared several chromene derivatives VIII bearing polyoxyethylenated groups and sugar residues at the C-8 position (12). 

Two of the better known "anti-juvenile "Hormone" agents, preco-cenes (9) and fluoromevalonate (10) are inhibitors of JH biosynthesis. The mode of action of fluoromevalonate at the molecular level is unknown. Elucidation of the mode of action of precocenes indicates that these plant chromene derivatives reach the site of JH biosynthesis, the corpora allata (CA), where they undergo a lethal epoxidation leading to extensive macromolecular alkylation and ultimately cause cell death (11, 12). Bioactivation of precocenes to the highly reactive precocene epoxide (13) in the corpora allata is almost certainly catalyzed by methyl farnesoate (MF) epoxidase (14), a cytochrome P-450 sonooxygenase (15) tdtich is the last enzyme of the JH biosynthetic pathway (at least in locusts and cockroaches). 

Two new chromene derivatives have been isolated from the aerial parts of A. annua. Their structures were resolved through normal NMR spectra as 2,2-dihydroxy-6-methoxychromene (84) and 2,2,6-trihydroxychromene (85). ... 

It was shown in the laboratory of P.T. Kaye that the reactions of 2-hydroxybenzaldehydes and 2-hydroxy-1-naphthaldehydes with various activated aikenes proceeded with regioseiective cyclization under Baylis-Hillman conditions to afford the corresponding 3-substituted 2H-chromene derivatives in high yields. Previous attempts to prepare 2H-chromenes chemoselectively via the cyclization of 2-hydroxybenzaldehyde-derived Baylis-Hillman products had proven unsuccessful. Complex mixtures containing coumarin and chromene derivatives were obtained. Good results were observed after the careful and systematic study of the various reactants and reaction conditions. 

M.G. Finn and co-workers developed a procedure for the preparation of 2/-/-chromene derivatives that includes a Petasis three-component reaction between salicylaldehyde, vinylic- and aromatic boronic acids, and dibenzylamine. The hydroxyl group of the salicylic aldehyde is essential for the activation of the boronic acid. The initially formed allylic amine undergoes a cyclization upon ejecting the dibenzylamine, thus rendering the process catalytic in the amine. 

Kaye, P. T., Nocanda, X. W. A convenient general synthesis of 3-substituted 2H-chromene derivatives. J. Chem. Soc., Perkin Trans, 1 2002, 1318-1323. 

Other reports have dealt with the photochromism of the acridine spiropyrans (53) and of several chromene derivatives, (54) and (55)7 In some instances the photochromic properties are poor. The influence of heteroatoms and ring size upon the photodegradation of some [2H]-chromenes has been investigated. A study of the photochromism of some 2,2-diarylsubstituted pyridoannelated [2H]-chromenes has been published. Photochromism is also exhibited by the indolino-naphthoxazine (56) in toluene. The photo-chromicity of 1,3,3-trimethylspiro[indoline-2,3 -[3H]-naphth-[2,1 -b][l, 4]-... 

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