Synthesis of Methoxynor Polyisoprenoid Alcohols by Alkylation of (3-Methoxyallyl)lithium Reagents

2002 ◽  
Vol 67 (1) ◽  
pp. 55-74 ◽  
Author(s):  
Qingwu Jin ◽  
Robert M. Coates
Keyword(s):  
Liquid Ammonia ◽  
Displacement Method ◽  
Enol Ether ◽  
Cyclization Reactions ◽  
Terpene Synthases ◽  
Substrate Analogs ◽  
Benzyl Ethers ◽  
Methoxy Substituent ◽  
The Stability ◽  
Transient Intermediates

A series of six methyl enol ether analogs 8-13 of geraniol, (E,E)-farnesol, and (E,E,E)-geranylgeraniol was synthesized from a group of three allylic methyl ethers and three allylic chlorides. Lithiation of the 1-methyl-, or 1-alkenylvinyl ethers with sec-butyllithium at -78 °C followed by alkylations of the resulting (Z)-(3-methoxyallyl)lithium reagents afforded the six possible Z-configured(trans) methoxynor polyprenyl benzyl ethers bearing the methoxy substituent at the internal and terminal double bonds with high Z/E ratios (5 : 1-31 : 1) and 47-80% yields. Reductive cleavage of the benzyl groups with lithium in liquid ammonia gave the corresponding methoxynor polyprenols. 11-Methoxy-18-nor and 7-methoxy-19-nor geranylgeraniols (13 and 12) were converted to the corresponding diphosphates, 7 and 32, by the Poulter displacement method. The stability of the enol ether in 7 in aqueous solution at pH 8 was verified by NMR analyses. The diphosphates of the methoxynor polyprenols may prove useful as substrate analogs for terpene synthases to capture transient intermediates in cyclization reactions catalyzed by these enzymes.

scholarly journals ALGORITHM AND SOFTWARE FOR CALCULATING THE STABILITY OF THE FORM OF EQUILIBRIUM OF DISCRETE SYSTEMS

2019 ◽  
Vol 13 (3) ◽  
pp. 44-49
Author(s):  
A.A. SHKURUPIY ◽  
A.N. PASCHENKO ◽  
P.B. MYTROFANOV
Keyword(s):  
Discrete Systems ◽  
Stability Loss ◽  
Transcendental Equation ◽  
Loss Of Stability ◽  
Displacement Method ◽  
Software Complex ◽  
Complex Functions ◽  
Transcendental Functions ◽  
The Stability ◽  
Theoretical Mechanics

The paper presents an algorithm for calculating the stability of the form of equilibrium of the first kind of compressed discrete systems by the method of displacements in combination with themethods of iterations and bisection. The use of the displacement method in combination with the iteration and bisection methods makes it possible to effectively determine the minimum critical stress or strain at the first bifurcation and their corresponding form of loss of stability, both for statically determined and statically undetectable systems. This approach, using matrixforms, makes it possible to significantly simplify the calculations of the analytical condition for the loss of stability of compressed discrete systems (the stability loss equation), which has high orders, as well as to construct the form of loss of stability corresponding to a critical load, that is, to solve the problem of loss of stability of equilibrium. The calculation of the compressed discrete system on the stability of the form of equilibrium actually reduces to the solution of the difficultly described nonlinear transcendental equation, which is the equation of loss of stability. The difficulty lies in the absence of an analytical solution of such an equation due to the presence of complex functions of Zhukovsky, which have transcendental functions in their structure. Such solution can be performed only with the use of numerical methods. This algorithm for calculating the loss of equilibrium of the first kind of compressed discrete systems by displacement in combination with the methods of iteration and bisection is implemented in the software complex "Persist" for a PC in Windows OS. The program was approbated and implemented in theeducational process at the Department of Structural and Theoretical Mechanics of the Poltava National Technical Yuri Kondratyuk University during the training of specialists in engineering specialties.

scholarly journals Unique thermodynamic relationships for Δf H o and Δf G o for crystalline inorganic salts. I. Predicting the possible existence and synthesis of Na2SO2 and Na2SeO2

2012 ◽  
Vol 68 (5) ◽  
pp. 511-527 ◽  
Author(s):  
Ángel Vegas ◽  
Joel F. Liebman ◽  
H. Donald Brooke Jenkins
Keyword(s):  
High Pressure ◽  
Solid State ◽  
Alkali Metal ◽  
Liquid Ammonia ◽  
Structural Changes ◽  
Target Material ◽  
The Other ◽  
Inorganic Salts ◽  
Linear Relationships ◽  
The Stability

The concept that equates oxidation and pressure has been successfully utilized in explaining the structural changes observed in the M 2S subnets of M 2SO x (x = 3, 4) compounds (M = Na, K) when compared with the structures (room- and high-pressure phases) of their parent M 2S `alloy' [Martínez-Cruz et al. (1994), J. Solid State Chem. 110, 397–398; Vegas (2000), Crystallogr. Rev. 7, 189–286; Vegas et al. (2002), Solid State Sci. 4, 1077–1081]. These structural changes suggest that if M 2SO2 would exist, its cation array might well have an anti-CaF2 structure. On the other hand, in an analysis of the existing thermodynamic data for M 2S, M 2SO3 and M 2SO4 we have identified, and report, a series of unique linear relationships between the known Δf H o and Δf G o values of the alkali metal (M) sulfide (x = 0) and their oxyanion salts M 2SO x (x = 3 and 4), and the similarly between M 2S2 disulfide (x = 0) and disulfur oxyanion salts M 2S2O x (x = 3, 4, 5, 6 and 7) and the number of O atoms in their anions x. These linear relationships appear to be unique to sulfur compounds and their inherent simplicity permits us to interpolate thermochemical data (Δf H o) for as yet unprepared compounds, M 2SO (x = 1) and M 2SO2 (x = 2). The excellent linearity indicates the reliability of the interpolated data. Making use of the volume-based thermodynamics, VBT [Jenkins et al. (1999), Inorg. Chem. 38, 3609–3620], the values of the absolute entropies were estimated and from them, the standard Δf S o values, and then the Δf G o values of the salts. A tentative proposal is made for the synthesis of Na2SO2 which involves bubbling SO2 through a solution of sodium in liquid ammonia. For this attractive thermodynamic route, we estimate ΔG o to be approximately −500 kJ mol−1. However, examination of the stability of Na2SO2 raises doubts and Na2SeO2 emerges as a more attractive target material. Its synthesis is likely to be easier and it is stable to disproportionation into Na2S and Na2SeO4. Like Na2SO2, this compound is predicted to have an anti-CaF2 Na2Se subnet.

The Stability of Pinacolates in Liquid Ammonia Solution

1936 ◽  
Vol 58 (1) ◽  
pp. 76-78 ◽  
Author(s):  
Charles Bushnell Wooster ◽  
Donald S. Latham
Keyword(s):  
Liquid Ammonia ◽  
Ammonia Solution ◽  
The Stability

Stability of the Vulcanized Cross-Link in Butyl Rubber: Theory and Application

1953 ◽  
Vol 26 (2) ◽  
pp. 356-369
Author(s):  
R. L. Zapp ◽  
F. P. Ford
Keyword(s):  
Analytical Data ◽  
Butyl Rubber ◽  
Cross Linking ◽  
Cross Link ◽  
Cyclization Reactions ◽  
Polymer Molecules ◽  
Whole Process ◽  
Sulfur Addition ◽  
The Stability ◽  
Competing Reactions

Abstract When rubberlike polymers are vulcanized with sulfur, the process involves two competing phenomena. The competing reactions are cross-linking and degradative in nature, and the conditions of vulcanization, as well as the extent, govern the rate at which these actions take place. At lower temperatures (110 to 150° C) vulcanizate degradation is held at a minimum, while higher temperatures usually accelerate the reversion process. A recent stoichiometric study of sulfur addition during Butyl rubber vulcanization revealed that the cross-link was composed of two atoms of sulfur. Calculations from analytical data placed the number of atoms at 1.7 to 2.2 per cross-link. This degree of constancy was maintained, regardless of the extent of vulcanization, until the onset of reversion. Reversion is the degradative process opposite to cross-linking. It can be pictured as the breakdown of the sulfur bridges between polymer molecules, and in Butyl it is evident at vulcanization temperature above 350° F. in 20 minutes. The type of rubber plays an important part in the relative way the two competing reactions occur. In addition, the whole process of cross-linking and reversion may be complicated by oxidative phenomena in predominantly diene type polymers. For example, when the vulcanization of natural rubber is prolonged, softening of the structure is followed by a hardening of the network, attributed to oxidation or cyclization. With Buna type rubbers, the softening action is barely evident before continued heating leads to a harder less extensible material As shown by Andrews, Tobolsky, and Hanson, the stress of a GR-S vulcanizate under intermittent strain increased on aging at 130° C. The stress of a Butyl sample remained essentially unchanged under the same conditions for about 10 hours, whereupon noticeable stress relaxation ensued. The use of an elastomer with a chemical unsaturation of 1 to 2 mole per cent of that found in polyisoprene reduces the opportunities for cyclization reactions. Observations on the stability of the sulfur cross-link can be made with less interference.

Metal-free synthesis of 1H-isochromenes via benzyl ether-assisted, electrophilic addition of diaryl acetylenes

2021 ◽  
Author(s):  
Tzu-Hsuan Kuan ◽  
Trimurtulu Kotipalli ◽  
Cheng-Chun Chen ◽  
Duen-Ren Hou
Keyword(s):  
Intramolecular Cyclization ◽  
Room Temperature ◽  
Electrophilic Addition ◽  
Benzyl Ether ◽  
Metal Free ◽  
Benzyl Ethers ◽  
The Stability ◽  
Diaryl Acetylenes

Bromotrimethylsilane (TMSBr) promoted, intramolecular cyclization of (o-arylethynyl)benzyl ethers to form 1H-isochromenes at room temperature is reported. Further studies indicated that the stability of vinyl carbocations is crucial, similar to the...

ChemInform Abstract: Calcium in Liquid Ammonia for the Reduction of Benzyl Ethers. Mechanistic Clues Derived from Chemoselectivity Studies.

ChemInform ◽  
1987 ◽  
Vol 18 (24) ◽  
Author(s):  
J. R. HWU ◽  
V. CHUA ◽  
J. E. SCHROEDER ◽  
R. E. JUN. BARRANS ◽  
K. P. KHOUDARY ◽  
...  
Keyword(s):  
Liquid Ammonia ◽  
Benzyl Ethers

An Approach to the Total Synthesis of Diterpenoid Plant Growth Substances Isolated From Gametophytes of the Fern Genus Anemia

1992 ◽  
Vol 45 (1) ◽  
pp. 227 ◽  
Author(s):  
CKF Chiu ◽  
LN Mander ◽  
AD Stuart ◽  
AC Willis
Keyword(s):  
Total Synthesis ◽  
Liquid Ammonia ◽  
Crystallographic Analysis ◽  
Aldol Reactions ◽  
Growth Substances ◽  
Enol Ether ◽  
X Ray ◽  
Relative Stereochemistry ◽  
Plant Growth Substances

Reduction of the oxoindan acid (9) by potassium in liquid ammonia followed by in situ alkylation with 3-methylbut-2-enyl bromide furnished enol ether (14) which was transformed into the acetal (17) and thence aldehydes (18; R = COCH3 and COCHCl2). Acid- catalysed aldol reactions then afforded the ethanoindene derivatives (19; R=COCH3 and COCHCl2). Further elaboration gave carbinol (28) which is envisaged as an intermediate for the total synthesis of the diterpenoid antheridiogens obtained from gametophytes of the fern genus Anemia, including acid (2). The relative stereochemistry of acetal (17) was established by X-ray crystallographic analysis.

Calcium in liquid ammonia for the reduction of benzyl ethers. Mechanistic clues derived from chemoselectivity studies

1986 ◽  
Vol 51 (24) ◽  
pp. 4731-4733 ◽  
Author(s):  
Jih Ru Hwu ◽  
Vincent Chua ◽  
Jean E. Schroeder ◽  
Richard E. Barrans ◽  
Kevin P. Khoudary ◽  
...  
Keyword(s):  
Liquid Ammonia ◽  
Benzyl Ethers

scholarly journals Chemical wizardry? The generation of diversity in terpenoid biosynthesis

2008 ◽  
Vol 80 (8) ◽  
pp. 1791-1798 ◽  
Author(s):  
Rudolf K. Allemann
Keyword(s):  
Recent Work ◽  
Chemical Reactions ◽  
Reaction Intermediates ◽  
Terpenoid Biosynthesis ◽  
Water Access ◽  
Cyclization Reactions ◽  
Terpene Synthases ◽  
Complex Chemical ◽  
Terpene Cyclase ◽  
Complex Chemical Reactions

Terpene synthases catalyze the conversion of linear prenyl-diphosphates to a multitude of hydrocarbon skeletons with often high regio- and stereoselectivity. These remarkable enzymes all rely on a shared fold for activity, namely, the class I terpene cyclase fold. Recent work has illuminated the catalytic strategy used by these enzymes to catalyze the arguably most complex chemical reactions found in Nature. Terpene synthases catalyze the formation of a reactive carbocation and provide a template for the cyclization reactions while at the same time providing the necessary stability of the carbocationic reaction intermediates as well as strictly controlling water access.

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