- Cleavage of tert-butyldimethylsilyl ethers by chloride ion
-
A general method for the selective cleavage of tert-butyldimethylsilyl ethers in the presence of tert-butyldiphenylsilyl ones has been established using a combination of H2O and a concentrated solution of LiCl in DMF at 90°C. Since no acids, bases, reducing or oxidizing agents are used, the method seems to be very appropiate for the deprotection of TBDMS ethers in the presence of other sensitive functional groups.
- Farras, Jaume,Serra, Carme,Vilarrasa, Jaume
-
p. 327 - 330
(2007/10/03)
-
- Telluroxide Elimination by Oxidation of Alkyl Aryl Tellurides: Remarkable Effect of Added Triethylamine
-
Treatment of various alkyl phenyl tellurides with 1-2 mol equiv. of m-chloroperbenzoic acid in diethyl ether in the presence of triethylamine at 25 deg C for 2 h affords the corresponding alkenes highly selectively in fair to good yields.From stereochemical studies using erythro- and threo-phenyl 3-phenylbutan-2-yl tellurides as substrates it was revealed that although Et3N partly faciliates E2 elimination of the telluroxide, the main reaction course is the telluroxide syn-elimination (Ei elimination).Without the addition of Et3N the elimination was quite slow in many cases, and in fact the compounds derived from the addition of m-chlorobenzoic acid to tetradecyl and cyclohexyl phenyl telluroxides were isolated, the pyrolysis (ca. 250 deg C) of which afforded tetradec-1-ene and cyclohexene, respectively.A 2-pyridyltelluro moiety was revealed for the first time to be a better leaving group than a phenyltelluro moiety in telluroxide elimination.
- Nishibayashi, Yoshiaki,Komatsu, Naoki,Ohe, Kouichi,Uemura, Sakae
-
p. 1133 - 1138
(2007/10/02)
-
- A refined method for the removal of the methoxymethyl (MOM) protecting group for carbinols with acidic ion-exchange resin
-
The methoxymethyl protecting group for carbinols is best removed from acid-sensitive substrates by hydrolysis in aqueous methanol using a cationic exchange resin (Dowex-50W).
- Seto,Mander
-
p. 2823 - 2828
(2007/10/02)
-
- Rates and Alkyl Group Size in Solvolysis of Alkyl Derivatives
-
The logarithm of solvolysis rate constants in 80percent aqueous ethanol of 1,1-dimethyl-1-alkyl chlorides 1 and 1-phenyl-1-alkyl chlorides 2 decrease monotonically with increasing number of carbon atoms in the alkyl group.The first member of both series deviates from the corresponding correlation lines which have the some slope.In contrast, solvolysis rates in 80percent aqueous ethanol of 1-methyl-1-alkyl tosylates 3 do not depend upon the size of the alkyl group.The results are rationalized in terms of a mechanism that is very similar in reactions of series 1 and 2 but different from that of series 3.
- Orlovic, Mirko,Kronja, Olga,Humski, Kresimir,Borcic, Stanko,Polla, Eugenio
-
p. 3253 - 3256
(2007/10/02)
-
- Shape Selective Alkane Hydroxylation by Metalloporphyrin Catalysts
-
A series of manganese and iron porphyrins with sterically protected pockets are shown to be shape selective alkane hydroxylation catalysts.With iodosobenzene as oxidant, good regioselectivity is observed for hydroxylation of alkanes at the least hindered methyl group by using the very sterically hindered (5,10,15,20-tetrakis(2',4',6'-triphenylphenyl)porphyrinato)manganese(III) acetate (MnTTPPP(OAc)) as catalyst; The moderately hindered (5,10,15,20-tetrakis(2',4',6'-trimethoxyphenyl)porphyrinato)manganese(III) acetate shows little selectivity toward terminal CH3 hydroxylation but does show enhancement for the adjacent, ω - 1, CH2 site.Primary selectivity is dependent on the size and shape of the alkane substrate, with more bulky substituents giving greater primary selectivity.Substituting pentafluoroiodosobenzene or m-chloroperbenzoic acid as oxidants yields similar selectivity, thus conclusively demonstrating metal based oxidation via a common intermediate for these three systems.In contrast, tert-butyl hydroperoxide or 2,2,2-trifluoroethanol solubilized pentafluoroiodosobenzene show no primary carbon selectivity, and reaction product ratios are independent of the metalloporphyrin catalyst; this demonstrates that the site of oxidation with these oxidants is not metal based.The iron porphyrin derivatives also show good primary selectivity, although to a lesser degree than with the Mn derivatives, proving that these oxidations too are metal based.The regioselectivities for alkane hydroxilation shown by TTPPP derivatives are comparable to or better than those found for some isozymes of cytochrome P-450 which are responsible for primary alcohol biosynthesis from steroids, fatty acids, and alkanes.
- Cook, Bruce R.,Reinert, Thomas J.,Suslick, Kenneth S.
-
p. 7281 - 7286
(2007/10/02)
-
- Shape-selective Alkane Hydroxylation
-
A series of sterically hindered manganese porphyrins have been used to catalyse shape-selective alkane hydroxylation, increasing the production of primary alcohols.
- Suslick, Kenneth,Cook, Bruce,Fox, Mary
-
p. 580 - 582
(2007/10/02)
-
- TELLUROXIDE ELIMINATION BY DIRECT OXIDATION OF ALKYL PHENYL TELLURIDE
-
Treatment of sec-alkyl phenyl tellurides, except for the cyclohexyl system, with m-chloroperbenzoic acid(MCPBA) in diethyl ether readily afforded the corresponding olefins in good yields presumably via telluroxide elimination together with small amounts of alcohols and ketones.In the pri-alkyl and cyclohexyl cases the adducts between MCPBA and the tellurides were isolated as stable organotellurium(IV) compounds which gave similar elimination products by neat pyrolysis at 220-250 deg C.
- Uemura, Sakae,Ohe, Kouichi,Fukuzawa, Shin-ichi
-
p. 895 - 898
(2007/10/02)
-
- New Aspects of the Telluroxide Elimination. A Facile Elimination of sec-Alkyl Phenyl Telluroxide Leading to Olefins, Allylic Alcohols, and Allylic Ethers
-
The utility of the telluroxide for olefin synthesis, a reaction which previously appeared to be of little value, is described.Treatment of sec-alkylphenyltellurium dibromides, except for the cyclohexyl system, with aqueous NaOH at room temperature affords olefins, allylic alcohols, and/or allylic ethers in high yields presumably via the formation of sec-alkyl phenyl telluroxides and their facile telluroxide elimination.As to the formation of linear olefins, more preference for elimination toward the less substituted carbon was observed than the selenoxide and sulfoxide eliminations.In the cyclododecyl case only trans-cyclododecene was formed as an olefin component in a sharp contrast to the selenoxide elimination that affords a 1:1 mixture of cis and trans isomers.On the contrary, in the n-alkyl and cyclohexyl cases the corresponding telluroxides are stable compounds that afford similar elimination products including vinylic ethers only by neat pyrolysis at temperatures above 200 deg C.
- Uemura, Sakae,Fukuzawa, Shin-ichi
-
p. 2748 - 2752
(2007/10/02)
-