Reductive dehydroxylation of allyl alcohols by IspH protein

The biosynthesis of natural products is a treasure trove of unusual reaction mechanisms. This Minireview summarizes recent work on the structure and mechanism of IspH protein, which catalyzes the reductive dehydroxylation of an allyl alcohol in a biosynthetic pathway leading to isoprenoid precursors.     

Rates of reaction between the nitrate radical and some unsaturated alcohols

Rate coefficients for nitrate radical gas-phase reactions with prop-2-en-l-ol (allyl alcohol), but-1-en-3-ol, and 2-methylbut-3-en-2-ol have been determined. Both absolute (fast flow discharge with diode laser detection of NO₃) and relative (batch reactor and FTIR spectroscopy) rate techniques were used to measure the rate coefficients. The rate coefficients at 294 K are: (1.3 ± 0.2) × 10⁻¹⁴, (1.2 ± 0.3) × 10 ⁻¹⁴, and (2.1 ± 0.3) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ for prop-2-en-1-ol, but-1-en-3-ol, and 2-methylbut-3-en-2-ol, respectively. The activation energy for reaction of NO₃ with prop-2-en-1-ol was determined to 2.8 ± 2.5 kJ mol⁻¹ in the temperature range between 273 and 363 K. The atmospheric importance of unsaturated alcohols and structure-reactivity considerations are also discussed. © 1996 John Wiley & Sons, Inc.     

Diastereoselective synthesis of unsaturated 1,2-amino alcohols from α-hydroxy allyl ethers using chlorosulfonyl isocyanate

Diastereoselective synthesis of 1,2-amino alcohols was achieved from a highly diastereoselective allylic amination reaction of α-hydroxy allyl ethers using chlorosulfonyl isocyanate. Diastereoselectivities varied depending on the stereochemistry of the ethers used and the stability of the carbocation intermediate obtained during the reaction. We propose that this CSI reaction is the results of either a S_Ni or S_N1 mechanism, according to the stability of the carbocation intermediate.     

Reductive cleavage of the halogen–phosphorus and sulfur–phosphorus bonds with alkali metals

The reduction of thiophosphorus acid chlorides with alkali metals (Na, K) in liq. NH₃/THF solution, potassium anthracenide, and potassium naphthalenide was investigated. It was found that these types of phosphorus compounds easily undergo reduction to >P S⁻ anions. It was also demonstrated that >P O⁻ and >P S⁻ anions as well very efficiently undergo sulfurization with elementary sulfur in liquid ammonia to yield >P(O)S⁻ and >P(S)S⁻ anions, respectively. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:330–339, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10040     

Stereochemistry of the iodocyclization of unsaturated alcohols

The corresponding tetrahydrofuran derivatives were obtained by iodination of , - unsaturated alcohols containing substituents attached to the -carbon atom. The effect of substituents on the stereochemistry of the products and the rate of iodination of the unsaturated alcohols were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 32–34, January, 1981.     

Reductive cleavage of N-O bonds using Samarium(II) iodide in a traceless release strategy for solid-phase synthesis

A strategy for making amides and ureas using a polymer-supported hydroxylamine resin as a traceless linker is described. The cleavage of the linker by samarium(II) iodide is reported for the first time.     

SmI2/water/amine mediates cleavage of allyl ether protected alcohols: application in carbohydrate synthesis and mechanistic considerations

[reaction: see text]. SmI2/H2O/amine provides selective cleavage of unsubstituted allyl ethers in good to excellent yields. This method is therefore useful in deprotection of alcohols and carbohydrates.     

碳碳不饱和键氟化加成反应的研究进展

选择性地向有机物中引入氟原子越来越受到重视，近年来通过碳碳不饱和键的 氟化加成来引入氟原子发展迅速。综述了碳碳不饱和键氟化加成反应的研究进展。     

Permanganate oxidation of unsaturated alcohols in alkaline media

A study was made on permanganate oxidation of olefinic and acetylenic alcohols in aqueous alkali media. Deprotonation constants of alcohols can be calculated from the kinetic data. The rate constant of alkoxide group oxidation exceeded that of the unsaturated bond. For oxidation of the alcoholic group a mechanism based on hydride ion transfer is proposed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 561–567, 2002     

Role of metal-oxo complexes in the cleavage of C-H bonds

The functionalization of C-H bonds has yet to achieve widespread use in synthetic chemistry in part because of the lack of synthetic reagents that function in the presence of other functional groups. These problems have been overcome in enzymes, which have metal-oxo active sites that efficiently and selectively cleave C-H bonds. How high-energy metal-oxo transient species can perform such difficult transformations with high fidelity is discussed in this tutorial review. Highlighted are the relationships between redox potentials and metal-oxo basicity on C-H bond activation, as seen in a series of bioinspired manganese-oxo complexes.     

Selective cleavage of the carbon-sulphur and carbon-oxygen bonds in methoxythioanisoles

Selective cleavage of thioether of ether functions in methoxythioanisoles in hexamethylphosphoramide (HMPA) with sodium gives methoxythiophenols by cleavage of the carbon-sulphur bond. Reactions with sodium isopropanethiolate give instead the thiomethoxyphenols by dealkylation of the methoxy function. When the methoxythioanisoles were treated first with sodium isopropanethiolate and then with sodium complete dealkylation was achieved with formation of mercaptophenols. The present methods have considerable advantages over existing procedures for the synthesis of methoxythiophenols, thiomethoxyphenols and mercaptophenols. The mechanistic implications of the reactions investigated are also discussed.     

Reductive cleavage of the C-O bond of acetals and orthoesters: reduction by silane in the presence of a Rh-PPh3 complex

Reductions of acetals to ethers and of orthoester to acetal by hydrosilane using rhodium catalyst are described.     

Regioselective bond cleavage and coordination effects in the reduction of some acetals with lithium in ammonia

Some benzylic-type acetals possessing the 2,8-dioxa-bicyclo [3.2.1]octane ring system are cleaved in a regioselective manner when treated with lithium in ammonia. The results f rom various reductions implicate coordination of lithium as a significant factor involved in reduction mechanisms.     

Polymerization of allyl esters of unsaturated acids. IX. Controlled ring closure in the radical cyclopolymerization of allyl methacrylate

Radical cyclopolymerization of allyl methacrylate (AMA) was investigated in detail, especially under the specified conditions; that is, above the ceiling temperature for a head-to-tail propagation (ΔG_ht ≥ 0) in the polymerization of methacrylate. Thus the structure of the polymer obtained was examined by ¹H- and ¹³C-NMR and infrared (IR) spectroscopy; no existence of unreacted pendant methacrylyl groups was observed, which suggests that, as a cyclopolymerization mechanism of AMA, intermolecular propagation of growing radicals, followed by intramolecular cyclization or intermolecular propagation of the resulting uncyclized methacrylyl radical, occurs exclusively with methacrylyl group. Temperature dependency of cyclization constant K_c was unusual; K_c increased rapidly at elevated temperatures and no linear relationship of ln K_c vs. 1/T was observed. Five-membered ring formation was favored at an elevated temperature and diluted monomer concentration. These results are discussed thermodynamically in terms of controlled ring closure in cyclopolymerization.     

Reductive cleavage versus hydrogenation of allyl aryl ethers and allylic esters using sodium borohydride/catalytic ruthenium(III) in various aqueous solvent mixtures

The reduction of allyl aryl ethers using sodium borohydride in the presence of a catalytic amount of ruthenium(III) chloride in various aqueous solvent mixtures at 0 °C was examined. In aqueous tetrahydrofuran, hydrogenation was the favored pathway (85-100% yield of the corresponding aryl propyl ether); whereas in aqueous N-methylformamide, reductive cleavage predominated (4:1 mixture of phenolic product/aryl propyl ether). In order to gain some insight into the mechanism for this process, 3-octyn-1-ol and trans-2-decen-1-yl acetate were subjected to similar reductive conditions; and both substrates afforded products inconsistent with a single-electron-transfer mechanism.