Tetrahydropyran THP

Using standard conditions for THP-protection, ethyl L-lactate is converted to the tetrahydro-2-pyranyloxy derivative 450 by reaction with dihydropyran in the presence of acid catalyst [141,142]. 

454 with dimethylamine furnishes (/ )-recipavrin with nearly complete inversion of the asymmetric center (96% ee). ( S)-Recipavrin is prepared from 454 by two consecutive inversion reactions, where the tosylate is first converted to bromide 455 and the bromide ion is displaced with dimethylamine (84% ee). 

Treatment of 456 with bromoethane gives the corresponding enantiomeric quaternary ammonium salt, emepronium bromide, which is an anticholinergic agent with effects similar to atropine. 

The related intermediate 453 has also been used to supply the chiral hydroxyl center of the hydroxynonenoic acid 458 [144]. This acid fragment is common to jaspamide and geodia-molide A, both of which are cyclodepsipeptides isolated from lower marine organisms (sponges). 

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The formation of unsymmetrical ethers from the reduction of aldehydes in the presence of tetrahydropyran (THP) ethers is reported (Eq. 182).340... 

Tetrahydropyran (THP), aldehyde etherification, 67-68 Tetralin compounds, 5-methoxytetralin reduction of substituted naphthalene, 132-133... 

While the notion that the alkoxides derived from aliphatic alcohols are poor nucleophiles toward 7r-allylmetal complexes has prevailed over the years, much progress made in the recent past has rendered the transition metal-catalyzed allylic alkylation a powerful method for the O-allylation of aliphatic alcohols. In particular, owing to the facility of five- and six-membered ring formation, this process has found extensive utility in the synthesis of tetrahydrofurans (THFs) (Equation (29))150-156 and tetrahydropyrans (THPs).157-159 Of note was the simultaneous formation of two THP rings with high diastereoselectivity via a Pd-catalyzed double allylic etherification using 35 in a bidirectional synthetic approach to halichondrin B (Equation (30)).157 The related ligand 36 was used in the enantioselective cyclization of a Baylis-Hillman adduct with a primary alcohol (Equation (31)).159... 

In the present communication the strontium salt of one-ended living polystyrene (SrS2) was studied In tetrahydrofuran (THF) and tetrahydropyran (THP), In order to check the validity of the triple Ion mechanism. The Ionic dissociation of SrS2 In THP was expected to be smaller than In THF and therefore It was thought that perhaps a contribution to the propagation from species, other than the free S anions, would be detectable. 

Based on these effects it was seen qualitatively that the relative amount of termination depends on the solvating power of the solvent. Least termination is found in DME, more in THF and even more in tetrahydropyran (THP)(46). However, as long as the absolute termination rate constants are not known, it cannot be excluded that these differences just arise from the dependence of the propagation rate constant on the solvent. From the abovemen-tioned effects and the similarity of the propagation rate constants it can be concluded that in THF the termination rate constant is higher for Na+ than for Cs+ as the counterion (47). 

Details of the Janda-Chen synthesis were as follows. A tetrahydropyran (THP) linker was attached to the NCPS support enabling attachment of alcohols via THP ether formation.13 The THP-NCPS resin 1 is derivatized with / -(+)-4-hydroxy-2-cyclopentanone 2, giving the THP ether-based resin 3, followed by coupling of the C13 20 fragment by enone-cuprate addition. The cuprate required was generated from the corresponding E-vinyl stannane 4. The resulting enolate was trapped as the silyl end ether... 

The cosolvents chosen for this study were urea (U), acetone (ACT), di-methylsulfoxide (DMSO), p-dioxane (D), piperidine (PD), morpholine (M), terf-butanol (TBA), and to a lesser extent acetamide (ACM). The study of the binary system was also extended to piperazine (PZ) and tetrahydropyran (THP). This choice of cosolvents is sufficiently varied to allow an examination of the various factors which influence the transfer functions. 

Certain cyclic ethers which will not homopolymerize will copolymerize with THF (25, 52). These cyclic ethers are stable five and six-membered ring compounds such as 2-methyltetrahydrofuran (2-MeTHF), and 1,4-dioxane (DOX). It is probable that 4-phenyl-l,3-dioxane (PhDOX), tetrahydropyran (THP), and 4-methyl-l,3-dioxolane (MDOL) which do not homopolymerize but which have been reported to copolymerize with BCMO (107, 108) would also copolymerize with THF. In the copolymerizations a correlation was again found between the basicity of the attacking ether and its reactivity with the cyclic oxonium ion. The... 

In a review of the motions of guest molecules in hydrates, Davidson (1971) indicated that all molecules between the sizes of argon (3.8 A) and cyclobutanone (6.5 A) can form si and sll hydrates, if the above restrictions of chemical nature are obeyed. Ripmeester and coworkers note that the largest simple structure II former is tetrahydropyran (THP) (C5H10O) with a van der Waals diameter of 6.95 A (Udachin et al., 2002). Closely following THP are m- and p-dioxane and carbon tetrachloride, each with a molecular diameter of 6.8 A (Udachin et al., 2002). Molecules of size between around 7.1 and 9 A can occupy sH, provided that the below shape restrictions are obeyed and a help gas molecule such as methane is included. 

Cyclic ethers with larger rings than epoxides include tetrahydrofuran (THF), tetrahydropyran (THP), and dioxane. Large-ring cyclic polyethers, called crown ethers, can selectively bind metal ions, depending on the ring size. 

Tetrahydropyran (THP) has been found to be a poor substrate in the present a-C-H hydroxyalkylation reaction (20% yield dr 80 20). This result seems to be related to the previous observation of the low susceptibility to hydrogen abstraction of THP. See Refs, [le, f). 

Pyrans (Oxanes) The six-membered cyclic ethers are commonly named as derivatives of pyran, an unsaturated ether. The saturated compound has four more hydrogen atoms, so it is called tetrahydropyran (THP). The systematic term oxane is also used for a six-membered ring containing an oxygen atom. 

A complete assignment of the H NMR data for tetrahydropyran (THP) 140 has been reported <1998J(P2)1751>. At room temperature the 400 MHz spectrum of THP in 1 1 CDCl3 CFCl3 consists of three multiplets at S 3.63, 1.64, and 1.57 in a ratio of 2 1 2 (H(2), H(4), and H(3)). At -85 °C, all of the resonances are resolved and the assignment of axial and equatorial protons is possible. This data, in conjunction with the previously reported study of the coupling constants of tetrahydropyran and comparison with cyclohexane data (Table 11) <1976JOC1380>, provide a complete picture of the NMR of tetrahydropyran. 

When potassium is reacted with B4H2R4 (R = rBu) in tetrahydropyrane (thp) for 3 days, a 7 3 mixture of the anions B4HR4 and B ILf is obtained. The anion B4HR4 is... 

Prandi [50] reported the preparation of methyl a-D-caryophylloside, a natural 4-C-branched sugar, in which the key step was diiodosamarium-promoted coupling reaction. As illustrated in O Scheme 30, C-C bond formation between the cmde acid chloride 106 and ketone 107 was mediated smoothly by Sml2 in tetrahydropyran (THP). Expected products were isolated in 63% yield and in a 8 Idiastereoisomeric ratio. Reduction of the major diastereomer 108 with sodium borohydride in methanol at 0 °C was very slow, but the expected 109 was eventually obtained in 73% yield after 24 h at room temperature. 

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