Furan-aceton reaction

Diphenylphthalazine N-oxide (458) when irradiated in acetone gives 1,3-diphenyI-benzo[c]furan. The reaction is thought to proceed through a diazoketone (459), which could be detected by IR spectroscopy (73JA7402). A similar decomposition of the diazoketone (460) to give the benzo[c]furan (461) has been reported (77LA116). 

Examples Compound <35) is a double diene, capable of Diels-Alder reactions on the simple diene and on the furan ring and it was required to try out a route to polycyclic compounds using both these reactions, Wittig disconnection direct to available aldehyde (36) and easily made (37) is possible, but the alternative Wittig disconnection to (38) takes advantage of the known simple and high yielding condensation of acetone with (36). 

Titanium silicate molecular sieves not only catalyze the oxidation of C=C double bonds but can be successfully employed for the oxidative cleavage of carbon-nitrogen double bonds as well. Tosylhydrazones and imines are oxidized to their corresponding carbonyl compounds (243) (Scheme 19). Similarly, oximes can be cleaved to their corresponding carbonyl compounds (165). The conversion of cyclic dienes into hydroxyl ketones or lactones is a novel reaction reported by Kumar et al. (165) (Scheme 20). Thus, when cyclopentadienes, 1,3-cyclohexadiene, or furan is treated with aqueous H202 in acetone at reflux temperatures for 6 h in the presence of TS-1, the corresponding hydroxyl ketone or lactone is obtained in moderate to good yields (208). 

Allenyl alcohols have been used as starting materials for a different kind of dihydrofuran synthesis. This is a process with great generality and utility in total synthesis. An example of the process is shown in Eq. 13.43 [42]. Treatment of allenyl alcohol 133 with silver nitrate in aqueous acetone at room temperature leads stereospe-cifically to dihydrofuran 134 in excellent yield. A similar reaction occurs with allenyl ketones, leading to furans. The isomerization is known to take place with Rh(I) [43], Ag(I) [44, 45] Pd(II) [46], Au(III) [47, 48] Cu(I) [49] or Hg(II) [50, 51],... 

Highly enantioselective Mannich-type reactions of A-(2-hydroxyphenyl) aldi-mines with ketene trimethylsilyl acetals and of A-Boc-aldimines with acetyl acetone or furan are catalyzed by chiral phosphonic acids 9 derived from 3,3 -diaryl-(l )-BlNOL and POCI3 (Scheme 12.7). ... 

The epoxidation of heteroarenes such as furans and indoles generates very labile products, such that the reaction needs to be carried out at subambient temperature. For example, even at —20°C, the epoxide of 2,3-drmethylbenzofuran rearranges to the ortho-quinomethide (equation 5) . To characterize this epoxide by H-NMR spectroscopy, the fully deuteriated DMD-dg solution, prepared in acetone-dg, was employed for the oxidation and the epoxide was detected at —78 °C . Alkynes lead on epoxidation to a multitude of oxidation products (equation 6) thus, the reaction is synthetically hardly useful and, therefore, has been little studied . ... 

Diaryl- and tetraaryl-substituted furans such as tetraphenylfuran (384) for example, yield generally cw-diaroylethylenes such as 380, probably via intermediate ozonide formation.257 Secondary reactions seem to depend very much on the nature of the solvents. Thus, cis-dibenzoylstilbene (380) has been observed by direct photooxygenation of 384 in CS2 as well as by methylene blue-sensitized photooxygenation of 384 in methanol.257,258 However, when the latter reaction was carried out in acetone, epoxide 386 and the enolbenzoate 387 were obtained.258... 

Diels-Alder reactions of benzo[fc]furan-43-diones and benzo[b]furan-4,7-diones have been reported <99H(50)1137>. The activation of a C-0 bond in a Mn(C0>3 complexed benzo[i>]furan was examined <99AG2343>. The enzyme-catalyzed dealkylation of (+)-marmesin to the phototoxic psoralene (and acetone) has been investigated <99AG413>. A hi yielding synthesis of bidentate bisoxazoline DBFOX/Ph [(R,R)-4,6-dibenzofutandiyl-2 2 -bis(4-phenyloxazoline)] was developed. DBFOX/Ph was subsequently tested in enantio-selective conjugate radical additions onto 3-(3-phenyl-2-propenoyl)-2-oxazolidinone <99TA2417>. 

One of the best procedures for the synthesis of 1,3-diphenylbenzo[c]furan (138) consists of the reaction of 3-phenylphthalide (102) with phenylmagne-sium bromide, 2- especially when the reaction mixture is worked up in the presence of hydroquinone. The primary product can be isolated as colorless crystals with mp 145°C (decomposition above 100°C) in the presence of acid this unstable compound loses water very rapidly. The stereochemistry of the hydroxyphthalan is not known with certainty presumably the cis isomer (137a) is formed first. In deuterated acetone equilibrium with the trans isomer (137b) is established. ° For the synthesis of 1,3-diphenylbenzo [cjfuran, the hydroxyphthalan need not be isolated. 

Figure 6-4. The formation of a macrocycle from the reaction of acetone with furan. This provides a rare example of a high-yield, cyclisation which occurs at normal concentrations of the reactants. In fact, considerable care needs to be taken with this reaction, which may be explosive ...

In contrast, in the photolysis of3,6-diphenylpyridazine-N-oxide 28 (R1 = R2 = Ph), a mixture of 3-benzoyl-5-phenylpyrazole 31 and 2,5-diphenylfuran 32 is formed. Diazoketone 29 (R1 = R2 = Ph) undergoes two competing reactions (i) thermal internal cyclization into the pyrazole 31 or (ii) photoinduced formation of a carbene leading to the final furan 32 (Scheme 12.9) therefore, the product distribution depends heavily on the reaction conditions. Thus, the formation of pyrazole 31 (75%) is favored over that of furan 32 (3%) by irradiation in acetone in a Rayonet reactor equipped with lamps irradiating at 350 nm. On the other hand, by irradiation with a Hanovia immersion lamp the yield of 31 decreases to 27%, whereas the yield of 32 increases to 67%. Moreover, the exclusive formation of the furan derivative 32 (43%) was observed by irradiation in the Rayonet reactor at low temperatures (—65 °C) [27]. 

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