2- -4,4,5,5-Tetramethyl-l,3-dioxolane

Similarly, 5-methyl-2-furaldehyde was converted into 3,4,6-tri-deoxy-DL-hex-3-enopyranosides. 4,4,5,5-Tetramethyl-2-(5-methyl-2-furyl)-l,3-dioxolane was oxidized with bromine-water, and the unsat-urated dioxolane resulting was immediately reduced with sodium borohydride, to give a mixture of DL-2-(l,4-dihydroxy-cts-pentenyl)-4,4,5,5-tetramethyl-l,3-dioxolane. Methanolysis gave the known methyl 3,4-6-trideoxy-a-DL-threo- and -en/f/iro-hex-3-enopyranosides, identified by H-n.m.r. spectroscopy.24 ... 

It was possible to obtain from 2-acetoxy-4,4,5,5-tetramethyl-l-3-dioxolan [64] a solution in which more than 90% of it had been converted into... 

Breakdown of the hemiorthoester intermediate was also found to be rate-limiting in acidic solutions with substituted 2-phenyl-2-methoxy-1,3-dioxolans [71] (substituents p-MeO, p-Me, p-F, p-Cl, p-Br, m-Cl and p-NOz) (Ahmad et al., 1979), 2-phenyl-2-methoxy-4,4,5,5-tetramethyl-l,3-dioxolan [72] (McClelland et al., 1979a), the orthoester [73] derived from exo.exo-2,... 

The hydrolysis rates of 1,3-dioxolanes are decreased by substitution of four methyl groups at the positions 4 and 5. 2,4,4,5,5-Pentamethyl-l,3-dioxolane reacts 6.5 times more slowly than 2-methy 1-1,3-dioxolane [161]. The AS value is decreased by 9 eu. A Hammett p value of—2.0 has been found for the substituent effect on the hydrolysis of 2-phenyl-4,4,5,5-tetramethyl-l,3-dioxolane in dilute aqueous hydrochloric acid [167]. The data obey the simple Hammett equation, and it is not necessary to apply o+ values. For the reaction of the unsubstituted 2-phenyl-4,4,5,5-tetramethyl compound, the solvent isotope effect is kH/kD = 0.42, and AS is —14.2 eu. General catalysis by formic acid has been observed in the hydrolysis of the p-methoxy compound. However, the rate is not significantly increased by addition of strong nucleophiles. 

In a dry and argon-flushed flask, 4,4,5,5-tetramethyl-l,3-dioxolane-2-one 0-phenylsulfoxime (199 593 mg, 1.98 mmol) is dissolved in CH2CI2 (15 mL). 2-Methoxyphenylmagnesium bromide (solution in diethyl ether, 2.2 mmol) is added and the reaction mixture is stirred 30 min at 25 °C. The reaction mixture is cooled to 0 °C and quenched with pH 9 buffer. Standard workup gives the crude imine, which is dissolved in methanol (10 mL) and cooled to 0 °C. HCI (4 mL, 1 M in diethyl ether) is added and the mixture stirred 1.5 h at 25 °C. Volatile materials are removed in vacuo and dry diethyl ether (40 mL) is added. Filtration gives 2-methoxyaniline hydrochloride (200 305 mg, 96%) as a pale purple powder. ... 

Another representative example of a homolytic perester fragmentation is given by the thermal decarboxylation of y9-peroxylactones such as 4,4,5,5-tetramethyl-l,2-dioxolan-3-one [569] cf. Eq. (5-63). 

Tetramethyl-1,3-dioxolane, 466 4-Bromomethyl-l, 3 -dioxolane, 467 4-Phenylsulfonylmethyl-l,3-dioxolane, 467 4-(3-Butenyl)-l,3-dioxolane, 468 4-Phenyl-l,3-dioxolane, 468... 

The complex formed on addition of cuprous iodide to a solution of a lithium dialkylamide in ether or tetrahydrofuran is effective in the reductive coupling of allylic halides to give 1,5-dienes with preservation of stereochemistry. This method has been used5 for the stereospecific synthesis of all-trans-squalene and (E,Z,Z,E) squalene from (E,E)- and (Z,JE)-farnesyl bromides, respectively. In an attempted synthesis of (3S)-squalene-2,3-epoxide, 4-[(4R)-2,2,5,5-tetramethyl-l,3-dioxolan-4-yl]butan-2-one (1) and the phosphonium iodide (2) were prepared.6 Unfortu-... 

The cyclic dimerization of HIBA proceeded smoothly in the presence of the dehydration catalyst methane sulfonic acid to isolate the cyclic dimer TMG in a 67% 5deld. Another simple and convenient route for the s5mthesis of TMG from lactic acid has been reported [102]. This method involves three steps (1) one-step protection of lactic acid hy cyclic acetalization employing acetone (2) cc-methylation of the obtained 2,2,5-trimethyl-l,3-dioxolan-4-one and [3] one-pot s5mthesis of TMG including the hydrolysis of 2,2,5,5-tetramethyl-l,3-dioxolan-4-one, resulting in moderate 5deld [49-51%] of TMG. 

Diamino-2,7-bis(l,3-dioxolan-2-yl)-4,5-dimethyloctane (68) [a bis(cycloa-cetal) of the corresponding dialdehyde] gave 2,4a,6,8a-tetramethyl-3,4,4a,7,8,8a-hexahydro-l,5-naphthyridine (69) (1M H2SO4 no details).196... 

Fig. 9.59 Plot of temperature of maximum spherulite growth rate, Tmax, against equilibrium melting temperature. I m, for indicated polymers. (1) isotactic poly(styrene) (a) (2) poly(tetramethyl-p-silphenylene siloxane) (b) (3) poly(cis-isoprene) (c) (4) poly(caproamide) (d,e) (5) poly(L-lactic acid) (f) (6) poly(phenylene sulfide) (g,h) (7) poly(R-epichlorohydrin), poly(S-epichlorohydrin), poly(I-RS-epichlorohydrin) (i) (8) poly(ethylene terephthalate) (j,k,l) (9) poly(aryl ether ether ketone) (m,n) (10) poly(ethylene-2,6-naphthalene dicarboxylate) (n) (11) poly(3-hydroxybutyrate) (o) (12) isotactic poly(methyl methacrylate) (q) (13) poly(dioxolane) (r) (14) New TPI poly(imide) (s) (15) poly(methylene oxide) (t) (16) poly(cis-butadiene) (u) (17) poly(propylene oxide) (v,w) (18) poly(imide) BPDA - - 134 APB (x) (19) poly(imide) BPDA - -C12 (x) (20) syndiotactic poly(propylene) (y) (21) poly(3-hydroxy valerate) (z) (22) poly(ethylene succinate) (aa) (23) poly(aryl ether ketone ketone) (bb) (24) poly(phenylene ether ether sulfide) (cc) (25) poly(tetramethylene isophtha-late) (dd) (26) poly(hexamethylene adipamide) (e,ee) (27) poly(tetrachloro-bis-phenol-A adipate) (fQ nylon 6-10 (ee).

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