Author Topic: Journal Xenophobia  (Read 2526 times)

0 Members and 1 Guest are viewing this topic.

Rhodium

  • Guest
Journal Xenophobia
« on: May 23, 2003, 11:31:00 PM »
Great post!

I think the reason why very few are interested in chinese journals is because they are too lazy to scan trough the table-of-contents of lesser known journals to find novel things of interest, they merely follow references from other journal articles they happen to read - and as asian journals seldom are quoted (for precisely the reason above), people never read them.

Rhodium

  • Guest
Zn(BH4)2/Pyridine reduces carbonyl compounds
« Reply #1 on: May 24, 2003, 12:32:00 AM »
(Pyridine)(tetrahydroborato)zinc Complex, [Zn(BH4)2(py)], as a New Stable, Efficient and Chemoselective Reducing Agent for Reduction of Carbonyl Compounds

Bull. Korean Chem. Soc. 24(4), 453-459 (2003)

(http://journal.kcsnet.or.kr/publi/bul/bu03n4/453.pdf)

Abstract

(Pyridine)(tetrahydroborato)zinc complex, [Zn(BH4)2(py)], as a stable white solid, was prepared quantitatively by complexation of an equimolar amount of zinc tetrahydroborate and pyridine at room temperature. This reagent can easily reduce variety of carbonyl compounds such as aldehydes, ketones, acyloins, -diketones and ,-unsaturated carbonyl compounds to their corresponding alcohols in good to excellent yields. Reduction reactions were performed in ether or THF at room temperature or under reflux conditions. In addition, the chemoselective reduction of aldehydes over ketones was accomplished successfully with this reducing agent.

dioulasso

  • Guest
N-methylation of amines with Zn(BH4)2
« Reply #2 on: January 09, 2004, 06:31:00 PM »
Some may find this interresting (posted it here, since this was the most closely related thread still open...):




Use of Zinc Borohydride in Reductive Amination: An Efficient and Mild Method
for N-Methylation of Amines

Sukanta Bhattacharyya et. al.

J. Chem. Soc. Perkin Trans. 1, pp. 1-2 (1994)

(http://bobo_bee.tripod.com/Hive/papers/2_red_am.djvu)

An efficient method for the reductive methylation of amines using paraformaldehyde, zinc chloride and zinc borohydride is described.




This can be an alternative to:

https://www.thevespiary.org/rhodium/Rhodium/chemistry/amphetamine.methylation.html



PiHKAL #109 MDMA

(http://www.erowid.org/library/books_online/pihkal/pihkal109.shtml)

Tihkal #50. NMT

(http://www.erowid.org/library/books_online/tihkal/tihkal50.shtml)

With this Zn(BH4)2 method nPr-NH2 is monomethylated w/ 70% yield.


Reductive amination w/ Zn(BH4)2 was discussed in:

Post 122811

(dormouse: "reductive amination with NaBH4 -- why *does* it work?  -rev drone", Serious Chemistry)


Post 69528 (missing)

(spric: "reductive amination with Zn(BH4)2", Methods Discourse)



Preparations of Zn(BH4)2


Post 394840

(demorol: "Preparation of zinc borohydride solution", Novel Discourse)



Lego

  • Guest
Zn(BH4)2/Pyridine also reduces COOH, Pt. 1
« Reply #3 on: January 31, 2004, 03:26:00 AM »
J. Chem. Res., 2003, 8, 522-525
No DOI found

Mild and convenient method for reduction of aliphatic and aromatic carboxylic acids and anhydrides with (pyridine)(tetrahydroborato)zinc complex as a new stable ligand-metal tetrahydroborate agent

Behzad Zeynizadeh and Karam Zahmatkesh

Department of Chemistry, Faculty of Sciences, Urmia University, Urmia 57159-165, Iran


Abstract: Structurally different aliphatic and aromatic carboxylic acids and anhydrides are efficiently reduced to their corresponding alcohols with a new modified zinc tetrahydroborate agent, (pyridine)(tetrahydroborato)zinc complex, [(Py)Zn(BH4)2], in refluxing THF.


Keywords: reduction, zinc tetrahydroborate, carboxylic acids, anhydrides, pyridine


Although, there are numerous literature references to the synthetic applications of various metal borohydrides,1 only sodium borohydride has gained commercial status in spite of its poor selectivity and lesser reactivity in organic solvents. Moreover, this reagent is invariably used in excess quantities. In order to affect the reactivity of sodium borohydride, many modifications have been made upon the reagent and so various modified borohydride agents are introduced for different reduction purposes. Recently, the preparation and applications of these reagents in organic synthesis have been reviewed.2
In fact, the reducing ability of borohydrides can be modified by: (a) hydride exchange with other substituents,3 (b) changing of sodium cation to other metal cations,4 quaternary ammonium5 and phosphonium cations,6 (c) a concurrent cation and hydride exchange,7 (d) preparation of ligand-metal borohydrides,8 (e) combination of borohydrides with metals, metal salts, Lewis acids;9 and, finally, (f) supporting on polymers.10
Among the reported transition metal borohydrides, zinc tetrahydroborate, Zn(BH4)2, is the only reagent which has been used frequently in the reduction reactions.11 However, because of its requirement for storage in a cold place and instability in solid state or solution for a long time, it should always be used as its freshly prepared ethereal solutions and this situation puts some restrictions on its uses. Recently new modifications of zinc tetrahydroborate in the form of ligand–metal complexes such as [(pyz)Zn(BH4)2]n12, [(dabco)Zn(BH4)2]2c,6b and [(Ph3P)x- Zn(BH4)2] (x=1, 2)13 have been introduced and their applications in the reduction of different functional groups have been reported. These successes prompted us to prepare (pyridine)-(tetrahydroborato)zinc complex, [(Py)Zn(BH4)2], as a new modified and stable zinc tetrahydroborate agent and investigate its reducing abilities.14 In our preliminary investigation, we reduced structurally different aromatic and aliphatic nitro compounds efficiently to their corresponding amines.14b In continuation of our experiments, now we wish to report an efficient method for the reduction of aliphatic and aromatic carboxylic acids and anhydrides to their corresponding alcohols in refluxing THF (Scheme 1).

Synthetic transformation of carboxylic acids to alcohols is one of the most important reactions in organic synthesis and this goal has been achieved by several borohydride combination systems.15-23 Zinc tetrahydroborate24 alone or its combination system with trifluoroacetic anhydride (TFAA)25 are the only reports of transition metal borohydrides that can reduce different aliphatic and aromatic carboxylic acids to their alcohols.



RCO2H/(RCO)2O ---(Py)Zn(BH4)2/THF/Reflux/85-97%--> RCH2OH
R: Alkyl, Aryl, Heteroaryl

Scheme 1


However, reduction reactions with these systems as mentioned above have some drawbacks. In the line of our interests for the preparation of new stable reducing agents on the base of zinc tetrahydroborate2c,12,13, we synthesised (Py)Zn(BH4)2. This reagent is easily prepared in almost quantitative yield by the complexation of 1:1 pyridine and Zn(BH4)2 in ethereal solution at room temperature (Eqns. (1) and (2)).

ZnCl2 + 2NaBH4 ---Dry ether--> Zn(BH4)2 + 2NaCl                   (1)
Zn(BH4)2 + Pyridine --> Pyridine.Zn(BH4)2                   (2)


This white stable reducing agent can be stored for months in a sealed bottle without losing its activity. It is not hygroscopic or light sensitive. Structural determination of the reagent was accomplished by the atomic absorption technique, volumetric assay and elemental analysis leading to its formula as (Py)Zn(BH4)2.
Investigation of reduction reactions with this system showed that the reagent can easily reduce variety of aliphatic, aromatic and heteroaromatic carboxylic acids to their corresponding alcohols with 2–4 molar equivalents of the reagent under reflux condition. Because of the better efficiency and reactivity of the reagent in THF, this was a solvent of choice. The results of this facile reduction are summarised in Table 1 and the corresponding alcohols were obtained in high to excellent yields (90–97%). As it is evident from Table 1, the reducing agent tolerates a number of other functional groups like halogen, methoxy and nitro groups in the molecules. Reduction of cinnamic acid gives the corresponding a,ß-unsaturated alcohols leading to the olefinic groups being unaffected (Entry 8). It is interesting to note that this contrasts with the behaviour of this substrate with LiAlH4 where it gives 1-phenylpropanol,26 by Zn(BH4)2/TFAA25 where there is no reduction and by Zn(BH4)224 alone where the major product with accompanying double bond reduction is a mixture of 1,2-diol and 1,3-diol (ratio: 3/2) of 3-phenylpropanediol (Table 2, Entry 4). Moreover, the olefinic groups are not affected when away from the carboxylic groups. For example oleic acid on reduction with this reagent gives oleyl alcohol (entry 16). It has been reported that dicarboxylic acids react with borane reagents27 to give the polymeric insoluble intermediates leading to incomplete reductions. However, in some cases the corresponding lactone is the major product.28 Our reducing agent completely reduces diacids such as terephthalic acid and trans-1,4-cyclohexanedicarboxylic acid to the correspon-ding diols in high yields (Entries 13 and 15). To highlight the limitations and advantages of our method, we compared some of our results against those of reported reagents (Table 2).
In other attempt, we also compared the efficiency of isolated (Py)Zn(BH4)2 with the addition effect of pyridine to the tetrahydrofuran solution of Zn(BH4)2 in the reduction of benzoic acid. The obtained results show that at a similar time in both procedures, the isolated reagent has higher rate and efficiency in comparison to the in situ procedure.

In exploring further the synthetic utility of this reducing agent we also found that symmetric aliphatic and aromatic anhydride carboxylic acids are efficiently reduced with 2–4 molar equivalents of the reagent in refluxing THF. The corresponding alcohols were obtained in high to excellent yields (85–96%).

The results of this type of reduction are summarised in Table 3 and we see that the aliphatic anhydrides are reduced faster than aromatic ones with low molar ratios of the reagent.

In conclusion, the usefulness of this methodology lies in the fact that pyridine stabilises Zn(BH4)2 in the form of (Py)Zn(BH4)2 for easy handling and storage. This new stable ligand-metal borohydride can efficiently reduce a variety of aliphatic, aromatic and heteroaryl carboxylic acids under mild condition. Reduction of diacids and conjugated or non-conjugated compounds to their alcohols was easily achieved without affecting the olefinic bond and formation of polymeric compounds. This reagent also efficiently reduces anhydride carboxylic acids with fast reduction of aliphatic compounds relative to the aromatic ones. Stability of the reagent relative to Zn(BH4)2, a simple procedure, mild reaction conditions, easy work-up of the reaction mixture and the high yields of the products are noteworthy advantages of this system and make it a useful addition to the present methodologies in this area.


Rhodium

  • Guest
Nitroalkene Reduction with Zinc Borohydride
« Reply #4 on: May 31, 2004, 03:26:00 AM »
Reduction of Conjugated Nitroalkenes with Zinc Borohydride.
A Mild Method for Converting Monosubstituted Nitroalkenes to Nitroalkanes and Disubstituted Ones to Oximes

Brindaban C. Ranu and Rupak Chakraborty

Tetrahedron 48(25), 5317-5322 (1992)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/znbh4.nitroalkenes2oximes.pdf)

Abstract
Mono-?-substituted conjugated nitroalkenes are readily reduced by zinc borohydride in 1,2-dimethoxyethane to the corresponding nitroalkanes, whereas the disubstituted ones furnish the corresponding oximes in excellent yields.


Rhodium

  • Guest
Reductive Amination with Zinc Borohydride
« Reply #5 on: October 18, 2004, 03:59:00 AM »
Reductive Amination with Zinc Borohydride. Efficient, Safe Route to Fluorinated Benzylamines
Sukanta Bhattacharyya, Arindam Chatterjee and John S. Williamson

Synthetic Communications 27(24), 4265-4274 (1997)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/redamin.znbh4.fluorobenzylamines.pdf)

Abstract
Fluorinated benzylamines are synthesized in high yields by reductive alkylation of secondary amines with appropriate fluoroaldehydes using a combination of zinc chloride and zinc borohydride. The present method method offers an alternative to toxic sodium cyanoborohydride and is adaptable to multigram-scale preparations.