Tris-tetrahydropyran

An iterative sequence of propargylation, enantioselective epoxidation of the resulting silylated skipped enynes, an endo selective hydroxyepoxide cyclisation and protodesilylation in which a SiMes group plays a pivotal role produces the tris-tetrahydropyran 9 in 18 steps <03OL2339>. The stereoselectivity of the endo selective oxacyclisations of 1,4-di- and... 

Zur Spaltung von Tetrahydrofuran-Ringen kann auch Lithium-tri-tert.-butyl-oxy-hydrido-aluminat/Triathyl-boran verwendet werden. Die Reaktion wird in Tetrahydropyran durchgefiihrt, das vom Reagens nur langsam angegriffen wird. 

This article deals with the conformational analysis of substituted oxanes (tetrahydropyranes) and derivatives in which ring methylenes are replaced by further oxygen atoms (di-, tri-, tetroxanes, pentoxanes, and O ) or by carbonyl group(s) (oxanones, Meidrum s acid derivatives) and, if conforma-tionally of interest, systems incorporating these rings in polycyclic structures... 

Some relevant monomers (6-8) showed a similar tendency they gave the polymers predominantly, but not entirely, composed of the respective cis-2,6-linked tetrahydropyran units, i.e., (1 ->6)-P-linked polysaccharide, when they were allowed to polymerize with lower initial monomer concentrations and at higher polymerization temperature. [13, 14] This is contrasted to l,6-anhydro-2,3,4-tri-0-benzyl-P-D-allo-pyranose (9), the D-enantiomer of 2(a), 3(e), 4(a)-tris(benzyloxy)-6,8-dioxabi-cyclo[3.2.1]-octane, which provided a polymer composed of frcns-2,6-linked tetrahydropyran units, i.e. (l- 6)-a-linked polysaccharide (10), when cationically polymerized. [15]... 

Ley and coworkers have found that dispiroketals383, such as 1,8,13,16-tetrahydro-oxadispiro[5.0.5.4] hexadecanes, show a wide range of synthetic applications554. For the preparation of these compounds, 2-(tri-n-butylstannyl)dihydropyrans can be used554-556. The reaction of 2-lithio-6-methyl-2-(phenylsulfanyl)tetrahydropyran (375) with tri-n-butylstannyl chloride gave compound 381, which has further been transformed into the dispiroketal 382 (Scheme 100)555. 

Among tetrahydropyran anhydrosugar derivatives the most common are 3,6-anhydro-pyra-noses. An example illustrating the synthesis of such types of compounds is the preparation of methyl 3,6-anhydro- -D-glucoside from methyl 2,3,4-tri-0-acetyl-6-bromo-6-deoxy-/3-D-gluco-pyranoside upon treatment with barium hydroxide. 3,6-Ahydro-D-galactose and 3,6-ahydro-D-mannose are prepared in a similar way (O Fig. 20). 

According to the procedure for the endo cyclization of the racemic epoxyalkyne derivatives, optically active cA-epoxide 60 was converted to the corresponding dicobalthexacarbonyl species, which was then treated with a catalytic amount of BF3-OEt2 in CH2CI2 at -78°C to afford the /ron.v-tetrahydropyran derivative 61 in 87% yield (Scheme 14). Demetalation of 61 with CAN was followed by protection of the secondary hydroxyl functionality with a silyl group to afford 62 in 87% yield. Upon consecutive treatment with tri- -butyltin hydride in the... 

The nature of the solvent and its polarity do not appear to affect in any regular way the position of the conformational equilibria for example, /3-D-xylopyranose tetrabenzoate, which exists in ace-tone-de (dielectric constant, e, = 20.7) as a 1 1 mixture of the CJ(d) and 1C(d) conformations, shows practically the same conformational population in a range of solvents, including benzene-rie = 2.3), toluene-dg ( = 2.4), chloroform-d (e = 4.8), pyridine-dg (e = 12.3), hexachloroacetone, and methyl sulfoxide-dg ( = 48.9). Similar results, showing negligible dependence of conformational populations on the polarity of the solvent, were obtained with jS-D-ribopyranose tetraacetate, tri-0-acetyl-/3-D-xylopyranosyl chloride, and some simpler derivatives of tetrahydropyran. In contrast, as the polarity of the solvent was increased, there was observed with methyl 2,3,4-tri-0-benzoyl-/3-D-xylopyranoside a broad trend in favor of that conformation having the C-1 substituent equatorially attached. 

In 2007, Schreiner applied his thiourea 8 in developing a green protocol for the protection of alcohols with tetrahydropyran (THP) under neat reaction conditions. Utilising the privileged A7,N -his[3,5-bis(tri-fluoromethyl)phenyl]thiourea and a polystyrene-attached analogue, high yields were observed even on a preparative scale. A remarkably broad substrate scope was examined, while high turnover numbers (100 000) and turnover frequencies (up to 5700 h ) were well established (Scheme 19.12). 

A soln. of 2,2,6,6-tetramethyl-4-cyano-l-oxa-2,6-disilacyclohexane in tetrahydro-furan added to a suspension of an intimate mixture of NaBH4 and quartz sand in abs. tetrahydropyran, BFg-tetrahydrofuran adduct then added drop-wise during ca. 0.5 hr., stirred and refluxed 1 hr. N,N, N"-tris-(2,2,6,6-tetra-methyl-l-oxa-2,6-disila-4-cyclohexylmethyl)borazine. Y 98%. W. Simmler, H. Niederprum, and H. Walz, B. 97, 1047 (1964). 

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