Di-tert-butyl dicarbonate: a versatile carboxylating reagent

Carbon nucleophiles generated by a non-nucleophilic base (LDA) were effectively trapped with di-tert-butyl dicarbonate (Boc-anhydride) to provide the corresponding tert-butyl aryl acetates, di-tert-butyl aryl malonates, unsymmetrical aryl malonates and tert-butyl benzoates in high yields. This reaction represents another useful way to prepare a variety of tert-butyl carboxylates and highlights the synthetic utility of di-tert-butyl dicarbonate as a versatile carboxylating reagent.     

An efficient synthesis of tert-butyl ethers/esters of alcohols/amino acids using methyl tert-butyl ether

A facile synthesis of a wide variety of tert-butyl ethers and tert-butyl ester derivatives under mild conditions is described. Alcohols etherified with tert-butyl methyl ether as tert-butyl source and solvent, in the presence of sulfuric acid. Many amino acid tert-butyl esters have been synthesized by this procedure. The reaction is simple, inexpensive, easily scaled up, and proceeds without observable racemization. A green method was developed for the deprotection of this group using Amberlite resin IR 120-H as catalyst.     

Kinetics of heat-induced and photochemical transformations of quinonimines and their derivatives

Heat-induced transformations of N-[2,6-diisopropylphenyl]-3,5-di(tert-butyl)-, N-[2,6-diethylphenyl]-3,5-di(tert-butyl)-, and N-[2-methyl-6-ethylphenyl]-3,5-di(tert-butyl)-o-benzoquinonimines in nonane follow the first-order rate equation, whereas that of N-[2,5-di(tert-butyl)phenyl]-3,5-di(tert-butyl-o-benzoquinonimine obey the second-order rate equation. Kinetic parameters of these reactions have been determined. 4aH-Phenoxazine derivatives of quinonimines are intermediates of the heat-induced transformations following the first-order kinetics; under the irradiation with 405 nm light they undergo the ring opening to give the starting compounds with quantum yield close to unity.     

A simple approach to the synthesis of dialkyl 5-tert-butylamino-[2,2′]bifuranyl-3,4-dicarboxylates

Reaction of tert-butyl isocyanide with electron-deficient acetylenic esters in the presence of N¹-[(Z)-1-benzoyl-3-oxo-3-phenyl-1-propenyl]-2-(2-furyl)-2-oxoacetamide leads to dialkyl 5-tert-butylamino-[2,2′]bifuranyl-3,4-dicarboxylates in moderate yields.     

Supramolecular self-assemblies of stereoisomers of p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups at the lower rim with some metal cations

Novel p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups at the lower rim in cone, partial cone and 1,3-alternate conformations were synthesized and their receptor properties toward metal ions of p- (Al³⁺, Pb²⁺) and d- (Fe³⁺, Co³⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺) elements were investigated by picrate extraction and dynamic light scattering (DLS). It was shown that the p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups are effective extractants of soft metal cations. The complex stoichiometry depended on the receptor configuration. All the p-tert-butyl thiacalix[4]arene derivatives with hydrazide fragments were able to form nanoscale aggregates but did not show self-association abilities.     

Dimeric water embedded within a hydrophobic cavity of tetra-(p-tert-butyl)thiacalix[4]arene

X-ray crystallographic analysis and density functional B3LYP/6-31G(d) calculation confirm that dimeric water is embedded within a hydrophobic cavity of tetra-(p-tert-butyl)thiacalix[4]arene and stabilized by hydrogen bondings of aromatic π?H₂O(1) and methyl?H₂O(2) in the dimeric water inclusion complex with binding energies of 1.4 and 0.9 kcal mol⁻¹ respectively, and by hydrogen bonding formed between H₂O(2) and four phenolic OH groups from an adjacent tetra-(p-tert-butyl)thiacalix[4]arene, with binding energy of 3.8-4.2 kcal mol⁻¹.     

Divergent synthesis of 6H-isoindolo[2,1-a]indol-6-ones and indenoindolones: an investigation of Pd-catalyzed isocyanide insertion

A novel Pd-catalyzed intramolecular cyclization via tert-butyl isocyanide insertion from 2-(2-bromophenyl)-1H-indoles has been developed, which demonstrates the utility of isocyanides in C–N or C–C bond construction. Treatment of 2-(2-bromophenyl)-1H-indoles with tert-butyl isocyanide affords 6H-isoindolo[2,1-a]indol-6-ones with high efficiency. However, N-methyl or N-Boc protected 2-(2-bromophenyl)-1H-indoles gives indenoindolones in excellent yields under the same condition, which reveals that under the described situation, isocyanides insertion for the formation of C–N bonds is prior to that of C–C bonds.     

A one-pot synthesis of a branched tertiary phosphine oxide from red phosphorus and 1-(tert-butyl)-4-vinylbenzene in KOH-DMSO: an unusually facile addition of P-centered nucleophiles to a weakly electrophilic double bond

Red phosphorus reacts with 1-(tert-butyl)-4-vinylbenzene in a superbase media (KOH-DMSO, 90-100 °C, 3 h) to give tris[4-(tert-butyl)phenethyl]phosphine oxide in 77% yield. Microwave activation of the reaction affords the phosphine oxide in 82% yield in 6 min.     

Synthesis and structure of 2,2′-spirobi(1,3-benzodioxole) derivative prepared from 3,5-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-1,2-benzoquinone

3,5-Di(tert-butyl)-1,2-benzoquinone reacted with 1,2,3-trimethylbenzimidazolium iodide led to the formation of 2,2′-spirobi[4,6-di(tert-butyl)-1,3-benzodioxole]. The reaction mechanism was suggested. The structure of 2,2′-spirobi[4,6-di(tert-butyl)-1,3-benzodioxole] was established by means of X-ray diffraction analysis.     

A synthesis of bicyclo[n.1.0]alkanes having tert-butyl carboxylate or acetamide moiety via the intramolecular 1,3-CH insertion of magnesium carbenoids

Treatment of 1-chlorovinyl p-tolyl sulfoxides, derived from various cyclic ketones and chloromethyl p-tolyl sulfoxide, with lithium enolate of carboxylic acid tert-butyl esters or N,N-dimethylacetamide gave adducts in high yields. The adducts were treated with ether solution of isopropylmagnesium chloride in dry toluene to give bicyclo[n.1.0]alkane derivatives having tert-butyl carboxylate or acetamide moiety on the bridgehead carbon in high to quantitative yields via magnesium carbenoid 1,3-CH insertion reaction. The 1,3-CH insertion reaction proved to be regioselective and stereospecific. The reaction mechanism and origin of the selectivity and specificity are discussed.     

Synthesis of polypeptide/inorganic hybrid block copolymers

Polypeptide/inorganic hybrid copolymers were obtained by a four-step synthetic approach combining (i) atom transfer polymerization of tert-butyl acrylate, (ii) chemical modification of the bromo end groups of ATRP-polymers into primary amino group using Gabriel reaction, (iii) ring opening polymerization of N_ε-trifluoroacetyl-l-lysine or γ-benzyl-l-glutamate N-carboxyanhydrides followed by (iv) the transamidification reaction using a large excess of (3-aminopropyl)trimethoxysilane to substitute the tert-butyl groups of the poly(tert-butyl acrylate) block. Products were characterized using ¹H NMR, FT-IR, DSC and MALDI-TOF MS. These techniques proved that polymerization of tert-butyl acrylate was controlled whatever the molecular weight targeted and that bromide was quantitatively converted to amino end group by a original method leading to the synthesis of copolymers in the presence of N-carboxyanhydrides as monomers. Amphiphilic polypeptide/inorganic hybrid copolymers were then achieved.     

Convenient removal of N-tert-butyl from amides with scandium triflate

Scandium triflate has been used as a convenient and efficient catalyst for removal of N-tert-butyl from amide groups. A variety of N-tert-butyl aryl and alkyl amides under these conditions gave the corresponding primary amide in high yields. With the use of microwave heating the deprotection reaction could be completed within 1 h.     

tert-Butyl isocyanide revisited as a convertible reagent in the Groebke-Blackburn reaction

tert-Butyl isocyanide can serve as the convertible reagent in Groebke-Blackburn multi-component reactions. The effective removal of the tert-butyl group from the resulting imidazo[1,2-a]azines and -azoles is achieved on a gram scale in two steps without chromatographic purification.     

An efficient method for the conversion of aromatic and aliphatic nitriles to the corresponding N-tert-butyl amides: a modified Ritter reaction

Aromatic and aliphatic nitriles react with tert-butyl acetate in the presence of a catalytic amount of sulfuric acid to give the corresponding N-tert-butyl amides in excellent yields.     

X-ray crystal structure of the tetra(tert-butyl)erbate anion and attempts to prepare tetravalent organolanthanide complexes

The new [Li(DME)₃⁺] salt of the previously-known tetra(tert-butyl)erbate(III) anion [Er(t-Bu)₄⁻] has been prepared and structurally characterized. The erbium(III) center is ligated by four tert-butyl groups in an approximately tetrahedral arrangement. The C–Er–C angles between the tert-butyl groups range from 108.8(3)° to 111.2(3)° and the Er–C distances range from 2.352(6) to 2.395(6) Å. The lithium cation is surrounded by three DME molecules, which form a distorted octahedral coordination sphere. Attempts to oxidize the analogous terbate complex [Li(DME)₃][Tb(t-Bu)₄] and its cerium analog to electrically neutral tetra(alkyl)lanthanide(IV) compounds are described.     

New synthesis of tert-butyl peroxycarboxylates

tert-Butyl peroxyacetate, tert-butyl peroxybutyrate, tert-butyl phenylperoxyacetate, and tert-butyl peroxyundecanoate were obtained in nearly quantitative yields by the esterification of the corresponding carboxylic acids with tert-butyl hydroperoxide in the presence of trifluoroacetic anhydride and pyridine in nonaqueous medium at 0–5°C. No tert-butyl peroxytrifluoroacetate was formed as a by-product during the process. A possible reaction mechanism is discussed.     

Chemoselective acylation of monosubstituted thiacalix[4]arene with di-<Emphasis Type="Italic">tert</Emphasis>-butyl dicarbonate

Mono-, di-, and tetrasubstituted derivatives of p-tert-butylthiacalix[4]arene containing tert-butylcarbamate, tert-butylcarbonate, and tert-butyl fragments have been prepared for the first time. Depending on the reaction conditions (reagents ratio, temperature, and the presence of a base), the interaction of the monoamine derivative of p-tert-butylthiacalix[4]arene with di-tert-butyl dicarbonate can lead to the formation of mono-, di-, and tetrasubstituted products.     

Convenient synthesis of 4-tert-butyl 2-ethyl 3-amino-1-benzyl-5-dialkylamino-1H-pyrrole-2,4-dicarboxylate derivatives

Optimization details and limitations of a novel synthetic method of 4-tert-butyl 2-ethyl 3-amino-1-benzyl-5-dialkylamino-1H-pyrrole-2,4-dicarboxylate derivatives are herein disclosed. This synthesis consists of four steps that include a highly selective cyclization, and can be carried out from starting materials to target compounds without column chromatography purification. The high selectivity is controlled by lithium coordination and steric hindrance caused by tert-butyl ester.     

Drastic solid-state fluorescence enhancement behaviour of imidazo[4,5-a]naphthalene-type fluorescent hosts upon inclusion of polyethers and tert-butyl alcohol

As one of the most promising materials for the construction of desirable solid-state fluorescent system, new solid-state fluorescent host-guest system, which consists of the imidazo[4,5-a]naphthalene-type fluorescent hosts 2 and sterically hindered guest molecules were designed and prepared. The crystals of 2 exhibit sensitive colour change and drastic fluorescence enhancement behaviour upon polyethers (diethylene glycol dimethyl ether (DGDM), diethylene glycol diethyl ether (DGDE) and diethylene glycol dibutyl ether (DGDB)) or tert-butyl alcohol. A comparison of the X-ray crystal structures of the guest-free and polyether- and tert-butyl alcohol-inclusion compounds indicates that the enclathrated polyether or tert-butyl alcohol molecule decrease the π-stacking between hosts and enlarge the distance between the host-host aromatic planes. On the bases of the spectral data and the crystal structures, the effects of the enclathrated sterically hindered guest on the drastic solid-state fluorescence enhancement behaviour of the host-guest crystals are discussed.     

Silicon-carbon unsaturated compounds. 77. Thermal behavior of cis- and trans-1-silacyclobut-3-ene formed from pivaloyl[tert-butylbis(trimethylsilyl)]silane and tert-butylacetylene

The reaction of tert-butylbis(trimethylsilyl)silyl potassium with pivaloyl chloride gave pivaloyl[tert-butylbis(trimethylsilyl)]silane (1) in 89% yield. The cothermolysis of 1 with tert-butylacetylene at 140 °C for 24 h produced the mixture consisting of cis- and trans-1,2,3-tri(tert-butyl)-2-(trimethylsiloxy)-1-(trimethylsilyl)-1-silacyclobut-3-ene (cis-2 and trans-2) in a ratio of 0.7: 1, in 88% combined yield. The thermolysis of the mixture, cis-2 and trans-2, at 250 °C for 24 h proceeded to give trans-1,2,4-tri(tert-butyl)-1-(trimethylsiloxy)-2-(trimethylsilyl)-1-silacyclobut-3-ene (4) as a single product in 96% yield. Similar treatment of cis- and trans-2 at 190 °C for 15 h afforded silylcyclopropene 3 quantitatively, which underwent further isomerization at 250 °C to give trans-1-silacyclobut-3-ene 4 in quantitative yield.