Solution ion pair structure of 2-lithio-1,3-dithianes in THF and THF-HMPA

Reich, Hans J.; Borst, Joseph P.; Dykstra, Robert R.

doi:10.1016/s0040-4020(01)90442-9

Cited by 42 publications

(15 citation statements)

References 55 publications

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“…NMR studies [13] of 2-lithio-1,3-dithiane and 2-lithio-2-methyl-1,3-dithiane then showed that these lithio derivatives were either monomeric or dimeric (sulfur-bridged) in THF solution at low temperature (Ϫ100°C), and cryoscopic measurements then indicated that 2-lithio-2-methyl-1,3-dithiane was largely monomeric in THF. [14] Moreover, more recent NMR studies by Reich [15] of 2-lithio-1,3-dithiane and of 2-tert-butyl-2-lithio-1,3-dithiane and 2-lithio-2-phenyl-1,3-dithiane have shown that all are monomeric contact ion pairs (CIPs) in THF/ Et 2 O mixtures (concentration of about 0.17 ), becoming separated ion pairs (SIPs) in the presence of excess HMPA.…”

Section: Addition Of Carbonyl Compounds To Lithio Derivative 5bn-limentioning

confidence: 99%

Diastereoreactivity of a Chiral Oxathiane Derived from 5‐Hydroxy‐1‐tetralone

2002

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The diastereoreactivity at the CH 2 bridge of a cis-oxathiane derived from 5-hydroxy-1-tetralone (unprotected and protected at the OH) was studied, and it appeared that all reactions at C-2 provided equatorial substitution. It was also found that: i) reductions of the equatorial benzoyl derivative with selectrides provided high diastereoselectivities at C-2Ј while LAH did not. Methyl Grignard addition was less selective and the selectivity of the propanoyl analogue was smaller; ii) condensation of aldehydes and/or ketones with the lithio derivative provided high equatorial diastereoselec-

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Section: Addition Of Carbonyl Compounds To Lithio Derivative 5bn-limentioning

confidence: 99%

Diastereoreactivity of a Chiral Oxathiane Derived from 5‐Hydroxy‐1‐tetralone

2002

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“…After considerable experimentation, we observed that the short-lived lithio dithiane could be generated almost instantaneously in the presence of (-)-41 with t-BuLi in 10% HMPA/THF at -78 °C. 55 In practice, premixing of (+)-40 and (-)-41 followed by exposure to t-BuLi furnished the C(30-42) fragment (-)-42 in 60% yield. Upon recognizing that 2-alkyl-1,3-dithiane anions are formed very rapidly (within ca.…”

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confidence: 99%

Total Synthesis of Immunosuppressants: Unified Strategies Exploiting Dithiane Couplings and σ-Bond Olefin Constructions

1998

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Although the immunomodulator cyclosporin A (CsA, 1) 1 has engendered dramatic progress in organ transplantation, recurrent clinical complications have stimulated an ongoing search for more potent and less toxic agents. The discovery of FK506 (2) 2 and the reinvestigation of rapamycin (3) 3 and demethoxyrapamycin (4) 4 heralded major advances in immunosuppressant research; not only are these natural products more potent than CsA, but they also selectively inhibit two distinct steps in the immune response. CsA and FK506, bound to immunophilins cyclophilin A and FKBP, respectively, prevent cells from entering the G 1 phase of the cell cycle, whereas the rapamycin-FKBP complex blocks progression into the S phase. The molecular biology, immunology and pharmacology of CsA, FK506, and rapamycin have been recently reviewed. 5 Discodermolide (5), first described in 1990, 6 displays immunomodulating activity intermediate between those of CsA and FK506. 7 In Burkitt lymphoma cells, discodermolide causes marked microtubule bundling, thereby arresting cellular development at the G 2 /M transition. 8 This mode of action is similar to that of Taxol, albeit its binding affinity is much higher than Taxol. As such, (+)-discodermolide could prove to be an effective therapeutic agent for the treatment of cancer. 8 The complex architecture and therapeutic importance of these nonpeptidal immunomodulators have attracted considerable interest among synthetic chemists, culmi- † This account is dedicated to

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“…Solvent-separated ion pairs are known to promote conjugate addition reactions, suggesting that sequestering the counterion would facilitate the cyclization. The cyclization did indeed proceed favorably when catalytic 12-crown-4 was added to the preformed anion, to provide a 4:1 ratio of indolizidines 3a and 3b in 90% yield (Scheme ).…”

Section: Resultsmentioning

confidence: 99%

α,β-Unsaturated Nitriles: Stereoselective Conjugate Addition Reactions

et al. 1997

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Dithiane anions undergo intramolecular conjugate additions with R, -unsaturated nitriles when a dithiane anion is tethered to N-1 of the 3-cyano-1,4,5,6-tetrahydropyridine nucleus. 3-Cyano-1-[2-(1,3-dithianyl-2-yl)ethyl]-1,4,5,6-tetrahydropyridine (1a) and the one-carbon homologue 1b cyclize in the presence of 12-crown-4 to generate indolizidine 3 and quinolizidine 9, in which the nitrile group exhibits a strong, thermodynamic preference for the axial orientation. Oxidation of 1b provides dithiane S-oxide 10 that undergoes a highly stereoselective conjugate addition to provide crystalline quinolizidine 13. The X-ray structure of 13 is reported and corroborates our "peg-ina-pocket" principle for stereoselective conjugate additions with R, -unsaturated nitriles.

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Solution ion pair structure of 2-lithio-1,3-dithianes in THF and THF-HMPA

Cited by 42 publications

References 55 publications

Diastereoreactivity of a Chiral Oxathiane Derived from 5‐Hydroxy‐1‐tetralone

Diastereoreactivity of a Chiral Oxathiane Derived from 5‐Hydroxy‐1‐tetralone

Total Synthesis of Immunosuppressants: Unified Strategies Exploiting Dithiane Couplings and σ-Bond Olefin Constructions

α,β-Unsaturated Nitriles: Stereoselective Conjugate Addition Reactions

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