Approaches to primary tert-alkyl amines as building blocks

Primary tert-alkyl amines include analogues of amantadine, a fragment commonly linked to pharmacophoric groups to enhance biological activity. The preparation of primary tert-alkyl amines is considered to be a difficult problem. Four synthetic procedures, some of which have been previously reported for the synthesis of amines with primary (RCH₂NH₂) or secondary (RR'CHNH₂) alkyl and/or aryl groups, were tested for the synthesis of primary tert-alkyl amines (RR′R″CNH₂) in aliphatic series including adamantane adducts. These procedures included the formation and reduction of tert-alkyl azides, the Ritter reaction in standard and modified conditions, the addition of organometallic reagents to N-tert-butyl sulfinyl ketimines and one-pot reactions between nitriles and organometallic reagents in the presence of a Lewis acid, Τi(iPrO)₄ or CeCl_3. These synthetic routes are unexplored for primary tert-alkyl amines. Studies on the synthetic routes for primary tert-alkyl amines are currently lacking. The reaction conditions and substrate limitations were studied for each procedure, with the first procedure being the most general and applicable also for compounds bearing bulky adducts.     

New tri-tert-alkyl substituted o-quinones of tetraline family

New tri-tert-alkyl substituted o-quinones of 3-tert-alkyl-5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalene-1,2-dione chemotype were obtained from phenol and 2,5-dichloro-2,5-dimethylhexane, with the SeO₂ oxidation of the sterically hindered phenol moiety having been performed at the final step. The electrochemical reduction of these quinones proceeds in two stages: the first reduction wave (E_1/2 = –0.60 ÷ –0.62 V) is reversible, while the second stage is irreversible.     

Synthesis of [μ-methyllenebis(η5-3-tert-butyl-2-methylinden-1-yl)dichlorozirconium(IV)]

An efficient synthetic approach to 3-alkyl(aryl)-2-bromoindenes was developed. The reaction of 2-bromo-3-tert-butylindene with MeMgl catalyzed by Ni(dppp)Cl₂ afforded 3-tert-butyl-2-methylindene from which bis(3-tert-butyl-2-methylinden-1-yl)methane and the correspondingansa-zirconocene were synthesized.     

Conversion of tertiary alcohols to tert-alkyl azides by way of quinone-mediated oxidation-reduction condensation using alkyl diphenylphosphinites

A novel method for the preparation of alkyl azides from alcohols by way of oxidation-reduction condensation is described. In this reaction, the sterically-hindered tert-alkyl phosphinites that are prepared from the corresponding alcohols are converted into tert-alkyl azides with almost complete inversion of their stereochemistry: the obtained alkyl azides are then successfully reduced to afford the corresponding amines on treatment with LiAlH₄, thus, a versatile method for the preparation of chiral amines from the corresponding chiral alcohols is established.     

Synthesis of (E)-2-(1-ferrocenylmethylidene)malonic acid derivatives by a cobalt-catalyzed domino reaction of ethyl diazoacetate, carbon monoxide and ferrocenylimines

The domino reaction of ethyl diazoacetate, carbon monoxide and ferrocenylimines was investigated in the presence of Co₂(CO)₈ as catalyst. In most cases the main products are 2-(1-ferrocenylmethylidene) malonates formed by an N(1)-C(4) cleavage of the primarily derived β-lactams. The latter compounds could only be isolated when the reaction was carried out at relatively low CO pressure, using an excess of ethyl diazoacetate. trans-N-(tert-Butyl)-3-ethoxycarbonyl-4-ferrocenyl-β-lactam proved to be the most stable one among these compounds and could be isolated in 55% yield. N-alkyl β-lactams were shown to undergo acidic cleavage leading to the E isomers of 2-(1-ferrocenylmethylidene) malonates as the main products. The structures of the two new compounds, (E)-2-ethoxycarbonyl-3-ferrocenyl-N-((R)-1-phenylethyl)-2-propenamide and trans-N-(tert-butyl)-3-ethoxycarbonyl-4-ferrocenyl-β-lactam were confirmed by X-ray crystallography. The relative thermodynamical stability of the products as well as the energetics of the acid-mediated cleavage of the β-lactam ring was elucidated with DFT calculations.     

First isolation of 1,3,2-dithiaphosphetane 2-sulfide

The treatment of tert-alkyl phenyl thioketones with Lawesson’s reagent (LR) gave two diastereomeric 1,3,2-dithiaphosphetane 2-sulfides in high yields. The structure of one of the major diastereomers was determined by X-ray crystallography. The reaction of 2-adamantanethione with LR yielded the corresponding spiro-1,3,2-dithiaphosphetane 2-sulfide derivative in 87% yield.     

One-step synthesis of pentavalent triphenylantimony derivatives Ph3Sb(OSiR3)2, Ph3Sb(OCH2CH2)2NH and Ph3Sb(OCH2CH2NMe2)2: X-ray molecular structure of Ph3Sb(OSiMe3)2

Pentavalent bis(triorganosiloxy)triphenylantimony derivatives, Ph₃Sb(OSiR₃)₂ (R = Me, Ph), were synthesized by reaction of triphenylantimony with trimethyl- or triphenylsilanol in the presence of tert-butylhydroperoxide by the mild reaction conditions (0-5 °C, 2 h). The reaction of triphenylantimony with diethanolamine in the presence of tert-butylhydroperoxide gave the cyclic compound Ph₃Sb(OCH₂CH₂)₂NH. The mixture of Ph₃SbO and Ph₃Sb(OCH₂CH₂NMe₂)₂ was obtained by the reaction of triphenylantimony with 2-(N,N-dimethylamino)ethanol in the presence of tert-butylhydroperoxide.     

Nature of solvation effects and mechanism of heterolysis of <Emphasis Type="Italic">tert</Emphasis>-alkyl halides

Specificities of heterolysis of tert-alkyl halides in protic and aprotic solvents were analyzed. Values of log k ₂₅ for heterolysis of tert-butyl chloride, tert-butyl bromide, tert-butyl iodiede, 1-chloro-1-methylcyclopentane, 1-chloro-1-methylcyclohexane, 1-bromo-1-methylcyclopentane, 1-bromo-1-methylcyclohexane, 2-chloro-2-phenylpropane, 1-iodoadamantane, and 2-bromo-2-methyladamantane in 19 to 44 solvents, determined mostly by the verdazyl technique were collected. Correlation analysis of solvation effects was performed in terms of multiparameter equations based on the linear free energy relationship principle, as well as in the logk-E _T coordinates. The nature of solvation effects and mechanism of heterolysis of a covalent C-Hlg bond were discussed.     

Kinetics of the reactions of tert-butanol with C2-C5 alcohols on sulfo cation exchangers

The kinetics of etherification of tert-butanol with aliphatic alcohols on gel KU-2×8 and macroporous KU-23 sulfo cation exchangers was studied. The first order of reaction with respect to tert-butanol and the -CSO₃H groups of a catalyst was established. The activation energy of the process observed on KU-2×8 was 60–95 kJ/mol. It was shown that the etherification of tert-butanol on KU-2×8 occurred in a surface layer. The reactivity of primary alcohols introduced into the reaction with tert-butanol increased with their molecular weights (C₂–C₅). The rate of reaction with secondary alcohols was lower than that with primary alcohols.     

Hydroxylamines and sulfinamide as amine components in the Petasis boronic acid-Mannich reaction: synthesis of N-hydroxy or alkoxy-α-aminocarboxylicacids and N-(tert-butyl sulfinyl)-α-amino carboxylicacids

An efficient synthesis of N-hydroxy or alkoxy-α-aminocarboxylic acids and N-(tert-butyl sulfinyl)-α-amino carboxylic acids has been developed from N,O-alkyl or hydroxylamines and tert-butyl sulfinamide utilizing a Petasis boronic acid-Mannich reaction. The scope and limitations of this method have been examined.     

Novel synthesis of 1,4-thiazin-2-one O-(tert-butyl) oximes and benzo[b][1,4]thiazin-2-one O-(tert-butyl) oximes in the presence of K2CO3/SiO2

A simple and efficient method was developed for the synthesis of 1,4-thiazin-2-one O-(tert-butyl) oximes and benzo[b][1,4]thiazin-2-one O-(tert-butyl) oximes from N-tert-butoxy acyl imidoyl bromides and 2-aminothiols in the presence of K₂CO₃/SiO₂. Twenty five novel compounds were readily synthesized in excellent yields using this procedure. The products possessed Z-stereochemistry with regard to the CN double bond. The reaction proceeded with initial substitution of bromine in the N-tert-butoxy acyl imidoyl bromides by mercapto groups in the presence of K₂CO₃/SiO₂, and subsequent intramolecular Schiff base formation.     

Indium-mediated mild and efficient one-pot synthesis of alkyl phenyl selenides

A mild and convenient one-pot process for synthesizing alkyl phenyl selenides is developed using indium metal. The reaction shows the selectivity for tert-alkyl, benzylic, and allylic halides over primary and secondary alkyl halides.     

Elucidation of methyl tert-butyl ether degradation with Fe/H2O2 by purge-and-trap gas chromatography-mass spectrometry

Degradation of methyl tert-butyl ether (MTBE) with Fe²⁺/H₂O₂ was studied by purge-and-trap gas chromatography-mass spectrometry. MTBE was degraded 99% within 120 min under optimum conditions. MTBE was firstly degraded rapidly based on a Fe²⁺/H₂O₂ reaction and then relatively slower based on a Fe³⁺/H₂O₂ reaction. The dissolved oxygen decreased rapidly in the Fe²⁺/H₂O₂ reaction stage, but showed a slow increase in the Fe³⁺/H₂O₂ reaction stage. tert-Butyl formate, tert-butyl alcohol, methyl acetate and acetone were identified as primary degradation products by mass spectrometry. A preliminary reaction mechanism involving two different pathways for the degradation of MTBE with Fe²⁺/H₂O₂ was proposed. This study suggests that degradation of MTBE can be achieved using the Fe²⁺/H₂O₂ process.     

Stereochemical aspects of the chemistry of 2-[trialkyl(aryl)silyloxy]alkyl-4-alkoxyalk-2-enylstannanes

2-tert-Butyldimethylsilyloxymethyl-4-(methoxymethoxy)pent-2-enyl(tributyl)stannane, prepared predominantly as the (Z)-isomer, is transmetallated by tin(IV) chloride to generate an allyltin trichloride which reacts with aldehydes with excellent stereocontrol in favour of (E)-1,5-syn-3-tert-butyldimethylsilyloxymethyl-5-(methoxymethoxy)alk-3-en-1-ols. These were taken through to 3-[(E)-2-(methoxymethoxy)-propylidenyl]-5-alkyl(aryl)tetrahydrofurans and used to prepare more complex 4-(methoxymethoxy)-pent-2-enylstannanes.     

Boron trifluoride-catalyzed reaction of alkyl fluoride with silyl enolate, allylsilane, and hydrosilane

Alkylation of silyl enolates with tert-alkyl or allylic fluorides proceeds smoothly in the presence of a catalytic amount of boron trifluoride to afford the corresponding carbonyl compounds. Allylation and reduction of alkyl fluorides with allylsilane and hydrosilane, respectively, occur under BF₃ catalysis.     

Oxidative dimerization of 2,6-Di-tert-butyl-4-(2-hydroxyethyl)phenol

2,6-Di-tert-butyl-4-(2-hydroxyethyl)phenol undergoes oxidative self-coupling by the action of K₃Fe(CN)₆ in alkaline medium at room temperature to give 7,9-di-tert-butyl-4-(3,5-di-tert-butyl-4-hydroxyphenyl)-1-hydroxymethyl-2-oxaspiro[4.5]deca-6,9-dien-8-one. The composition of the reaction products has been determined, and the mechanism of their formation is discussed.     

One-Step Synthesis of 3,4-Disubstituted 2-Oxazolidinones by Base-Catalyzed CO2 Fixation and Aza-Michael Addition

2-Oxazolidinones are saturated heterocyclic compounds, which are highly attractive targets in modern drug design. Herein, we describe a new, single-step approach to 3,4-disubstituted 2-oxazolidinones by aza-Michael addition using CO₂ as a carbonyl source and 1,1,3,3-tetramethylguanidine (TMG) as a catalyst. The modular reaction, which occurs between a γ-brominated Michael acceptor, CO₂ and an arylamine, aliphatic amine or phenylhydrazine, is performed under mild conditions. The regiospecific reaction displays good yields (av. 75 %) and excellent functional-group compatibility. In addition, late-stage functionalization of drug and drug-like molecules is demonstrated. The experimental results suggest a mechanism consisting of several elementary steps: TMG-assisted carboxylation of aniline; generation of an O-alkyl carbamate; and the final ring-forming step through an intramolecular aza-Michael addition.     

Generation of oxodiazonium ions 4. Nitramine O-alkyl derivatives in the synthesis of benzotetrazine-1,3-dioxides

A new method for the synthesis of benzotetrazine-1,3-dioxides was developed from the 2-(tert-butyl-NNO-azoxy)-N-nitroaniline O-alkyl derivatives upon the action of strong acids (H₂SO₄, MeSO₃H, CF₃CO₂H) or BF₃·Et₂O. A mechanism suggested for these reactions includes transformation of the N=N(O)OR group (R = Me, Prⁱ) to the oxodiazonium ion (N=N=O)⁺, which intramolecularly reacts with the neighboring tert-butyl-NNO-azoxy group, furnishing the tetrazine-1,3-dioxide ring.     

A Convenient Synthesis of Vinyl Sulfides

tert-Alkyl sulfides, with an α-(1H-benzotriazol-1-yl) group 6 and 13 , are readily prepared from N-[(aryl-thio)methyl]-1H-benzotriazoles 3 and N-( 11 ), respectively, by reaction with BuLi and then with the appropriate electrophile. The tert-alkyl sulfides 6 and 13 are smoothly converted by BF₃. OEt₂ into vinyl sulfides 5, 7 or 12 , respectively, in satisfactory yields.