Furans trimethylsilyloxy

Potential 2,5-dihydroxy compounds (185) exist in the dicarbonyl forms (186). Succinic anhydride (186 Z = O) on silylation is converted into 2,5-bis(trimethylsilyloxy)furan (187) the latter compound readily participates in Diels-Alder addition reactions (80TL3423). Reaction of thiosuccinic anhydride (186 Z = S) with the triphenylphosphorane Et02CH=PPh3 gives a product which exists in the aromatic form (188) (75LA1967). 

Furan, 2,5-bis(trimethylsilyloxy)-cycloaddition reactions, 4, 625 Diels-Alder reactions, 4, 77 synthesis, 1, 417 Furan, bromo-dipole moments, 4, 553 Furan, 2-bromo-electron diffraction, 4, 537 reactions, 4, 78 synthesis, 4, 604 Furan, 3-bromo-electron diffraction, 4, 537 Furan, 2-bromomethyl-5-nitro-reactions... 

In contrast, the titanium(IV)-catalyzed condensation of l-(trimethylsilyloxy)cydohexene and ( )-3-(2-nitro-l-propenyl)furan proceeded in the reverse stereochemical sense and gave three diastereomeric 1,2-oxazine 2-oxides lb, 2b and 3b in a ratio of 1 4 1. The major diastereomeric adducts 2b and lb were converted to the. syn-ketonc 4b upon hydrolysis16. 

Oxidation of 2-(trimethylsilyloxy)furan (301) with iodosobenzene in the presence of boron trifluoride etherate and alcohols or acids results in the formation of 5-substituted 2(5//)-furanones 303. The first step of this conversion gives intermediate 302, which on nucleophilic substitution by alcohols or acids affords the products (89TL3019) (Scheme 75). 

In regard to the importance of a diastereoselective synthesis of 5-[hydroxy(aryl) methyl]furan-2(5//)-ones, the Bi(OTf)3-4H20-catalyzed vinylogous Mukaiyama aldol has been investigated with 2-(trimethylsilyloxy)furans and various carbonyl compounds [146]. 

Initially, various solvents were screened for the Mukaiyama aldol reaction of benzal-dehyde with 2-(trimethylsilyloxy)furan in the presence of 1 mol% of Bi(0Tf)3-4H20. 

Table 16 Vinylogous Bi(OTf)3-catalyzed Mukaiyama aldol reactions involving benzaldehyde and 2-(trimethylsilyloxy)furan...

Conditions carbonyl compound (1.0 equiv.), 2-(trimethylsilyloxy)furan or 3-methyl-2-(trimethyl-silyloxy)furan (1.5 equiv.), Bi(0Tf)3-4H20 (x mol%), Et20, —45 °C, 0.5-3 h na not applicable... 

Attempts to isolate 2,3-dimethoxyfuran (156) have, as yet, been fruitless (79JCS(P1)1893), but it may be generated in situ and trapped with the propiolate (155) the initial adducts (157) are unstable under the acidic conditions and yield the biphenyls (158) and (159) (Scheme 67). 2,5-Bis(trimethylsilyloxy)furans, readily available from succinic anhydrides in one step, are also more reactive than furan in Diels-Alder reactions (80TL3423). They readily undergo reaction with both DMAD and ethyl acrylate. Thus at 50 °C in carbon tetrachloride the furan (160) with DMAD followed by detrimethylsilylation gave only the quinone (163). At 80 °C, however, the hydroquinone (164) is the major product. Both the intermediates (161) and (162) may be detected by ]H NMR spectroscopy. The formation... 

The cycloaddition reactions of 2,5-bis(trimethylsilyloxy)furans have been discussed (Section 3.11.2.7.1). The reactions of these compounds with aldehydes and ketones and with quinone acetals have also been investigated (80TL3431). 

Oxidation of 2-(trimethylsUyloxy)furan.1 Oxidation of 2-(trimethylsilyloxy)-furan with iodosylbenzene-BF3 etherate can afford 5-substituted 2(5//)-furanones. 

Regiocontrolled alkylation. The usual Lewis acids are ineffective for alkyla-t on of 2-(trimethylsilyloxy)furan (2), but use of several silver salts, of which 1 is the... 

Addition occurred in 2-trimethylsilyloxy-furan upon treatment with PhlO-BF3-Me3SiN3, with direct formation of 5-azidofuranone [99]. Some / -diketones and /j-ketoesters underwent a-azidation by PhIO-Me3SiN3 [100],... 

Diels-Alder cycloaddition between l,4,7-tris(trimethylsilyloxy)benzo[f]furan 174 and the dienophile 175 was also the key step in the total synthesis of (+)-dynemicin A 176 reported by Myers <1997JA6072>, as can be seen in Scheme 63. 

Cinchonidine-derived quaternary ammonium phenoxides (e.g., 296) have been shown to catalyze vinylogous aldol-type reaction between benzaldehyde and 4-methyl-2-(trimethylsilyloxy)furan, leading to the formation of a 5-substituted butenolide in good yield and good ee% as can be seen in Equation (181) <2007CL8>. 

DIELS-ALDER REACTIONS 3-Acetyl-4-oxazoline-2-one. 1,3-Bis(trimethylsilyl-oxy)-l,3-butadiene. 1-Chloro-l-di-methylaminoisoprene. 1,3-Dihydroiso-thianaphthene-2,2-dioxide. 4,6-Di-methoxy-2-pyrone. Furane. trans -Methoxy-3-trimethylsilyloxy-l,3-butadiene. Trichloroethyl trans-1,3-butadiene-1-carbamate. Trichloro-1,2,4-triazine. 

The chiral amine catalyst shown below was used to promote the asymmetric [4+3] cycloaddition between 2,5-disubstituted furans and trialkylsilyloxypentadienals to generate 7-membered carbocycles with enJo-selectivity and in a promising 89% ee <03JA2058>. Computational studies of the AICI3-catalyzed [4+3] cycloaddition between 2-(trimethylsilyloxy)acrolein and furan at the B3LYP/6-31G level showed that the reaction was a three-step process <03OL4117>. 

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