“…Diamine-bis(cyanoboranes) ( 1 ) were synthesized from a Me 2 S solution of cyanoborane (Scheme , i) in nearly quantitative (ca. 3-fold compared to ether, THF, and glyme solutions) yields, similarly to our synthesis of cyanoborane complexes of monobasic amines. , This improvement is probably due to the soft character of Me 2 S, which renders “BH 2 CN” more susceptible to base exchange. 1 …”
Section: Resultssupporting
confidence: 67%
“…A large number of amine carboxyboranes and their derivatives substituted on the carbon atom (amine·BH 2 X, where X = COOH, − COOR, − CONR 2 , ,, C(O)NHOH, CSNHR, C(OR)NR, C(CN)NR, etc.) have been synthesized in the past twenty years.…”
DA·2BH2CN (1) [DA = N,N,N‘,N‘-tetramethylethanediamine (TMEDA, a), N,N,N‘,N‘-tetramethylpropanediamine
(TMPDA, b), and N,N,N‘,N‘-tetramethylbutanediamine (TMBDA, c)], (DA·2BH2CNEt)(BF4)2 (2), and DA·2BH2COOH (3) complexes were prepared from Me2S solution of (BH2CN)
n
(→ 1 → 2 → 3) in fast procedures, differently
from those usually applied, in good yields. Dimethyl esters (4) were prepared from 3 with methanol in very fast
reactions catalyzed by HBr. 3 and 4 were transformed into DA·BH2COOH (5a,b) and DA·BH2COOMe (6) with
DA in THF. Bromination of 3 in aqueous HBr yielded diamine-bis(monobromocarboxyboranes) (7), in vigorous
conditions diamine-bis(dibromocarboxyboranes) (9) were produced. N-Bromosuccinimide in methanol transformed
3a,b directly into diamine-bis(bromomethoxycarbonylboranes) (8a,b). BrH·DA·BH(Br)COOH (10a,b) could be
prepared from 5a,b with bromine in strongly acidic medium. N-Deprotonated 10a quickly transformed into a
five-membered cyclic cation [TMEDA·BHCOOH]+ (cation in 12a) in both water and methanol. Thus, this ion
was formed by dissolution of 10a in water, bromination of 5a or destroying one of the borane moieties in 7a by
a base. N-Deprotonated 10b in water decomposed with a pH-dependent rate, but in methanol, in the presence of
base, it transformed into a six-membered cyclic cation [TMPDA·BHCOOH]+ (cation in 12b). 8a,b could also
be transformed into cyclic cations by destroying one of their borane moieties in methanol, (8b in absence of acids
only). All cations were prepared as bromide, hexafluorophosphate and tetraphenylborate salts. pK
a values of
12a,b (pK
a = 5.5−5.6) are 3 units lower than those of amine-carboxyboranes. Zwitterions (18a,b) formed by
their deprotonation were prepared. Cyclic cation [TMEDA·B(Br)COOH]+ (cation in 19a) formed on destroying
one dibromocarboxyborane of 9a. This cation, quite a strong acid (pK
a ≈ 4.2), was prepared as hexafluorophosphate
and tetraphenylborate salt. The latter was transformed with aqueous KOH into the corresponding zwitterion
(21a).
“…Diamine-bis(cyanoboranes) ( 1 ) were synthesized from a Me 2 S solution of cyanoborane (Scheme , i) in nearly quantitative (ca. 3-fold compared to ether, THF, and glyme solutions) yields, similarly to our synthesis of cyanoborane complexes of monobasic amines. , This improvement is probably due to the soft character of Me 2 S, which renders “BH 2 CN” more susceptible to base exchange. 1 …”
Section: Resultssupporting
confidence: 67%
“…A large number of amine carboxyboranes and their derivatives substituted on the carbon atom (amine·BH 2 X, where X = COOH, − COOR, − CONR 2 , ,, C(O)NHOH, CSNHR, C(OR)NR, C(CN)NR, etc.) have been synthesized in the past twenty years.…”
DA·2BH2CN (1) [DA = N,N,N‘,N‘-tetramethylethanediamine (TMEDA, a), N,N,N‘,N‘-tetramethylpropanediamine
(TMPDA, b), and N,N,N‘,N‘-tetramethylbutanediamine (TMBDA, c)], (DA·2BH2CNEt)(BF4)2 (2), and DA·2BH2COOH (3) complexes were prepared from Me2S solution of (BH2CN)
n
(→ 1 → 2 → 3) in fast procedures, differently
from those usually applied, in good yields. Dimethyl esters (4) were prepared from 3 with methanol in very fast
reactions catalyzed by HBr. 3 and 4 were transformed into DA·BH2COOH (5a,b) and DA·BH2COOMe (6) with
DA in THF. Bromination of 3 in aqueous HBr yielded diamine-bis(monobromocarboxyboranes) (7), in vigorous
conditions diamine-bis(dibromocarboxyboranes) (9) were produced. N-Bromosuccinimide in methanol transformed
3a,b directly into diamine-bis(bromomethoxycarbonylboranes) (8a,b). BrH·DA·BH(Br)COOH (10a,b) could be
prepared from 5a,b with bromine in strongly acidic medium. N-Deprotonated 10a quickly transformed into a
five-membered cyclic cation [TMEDA·BHCOOH]+ (cation in 12a) in both water and methanol. Thus, this ion
was formed by dissolution of 10a in water, bromination of 5a or destroying one of the borane moieties in 7a by
a base. N-Deprotonated 10b in water decomposed with a pH-dependent rate, but in methanol, in the presence of
base, it transformed into a six-membered cyclic cation [TMPDA·BHCOOH]+ (cation in 12b). 8a,b could also
be transformed into cyclic cations by destroying one of their borane moieties in methanol, (8b in absence of acids
only). All cations were prepared as bromide, hexafluorophosphate and tetraphenylborate salts. pK
a values of
12a,b (pK
a = 5.5−5.6) are 3 units lower than those of amine-carboxyboranes. Zwitterions (18a,b) formed by
their deprotonation were prepared. Cyclic cation [TMEDA·B(Br)COOH]+ (cation in 19a) formed on destroying
one dibromocarboxyborane of 9a. This cation, quite a strong acid (pK
a ≈ 4.2), was prepared as hexafluorophosphate
and tetraphenylborate salt. The latter was transformed with aqueous KOH into the corresponding zwitterion
(21a).
“…The synthesis of amine carboxyborane derivatives such as methyl ester of various amine carboxyborates have been described previously. Several esterification methods of amine carboxyboranes with alcohols include using DCC to make 98% yield (Spielvogel et al, 1986) and using a catalytic amount of hydrogen bromide, which provides nearly quantitative yields (Gyo ri et al, 1995). In our process, esterification is completed before the amine exchange reaction and not vice versa.…”
Hexamethylenetetramine carboacetaminophenborane, a molecule with two pharmacophores attached to a central carboxyborate moiety, was synthesized and crystals were grown with an acetaminophen co-crystal former to result in the title 1:1 co-crystal [hexamethylenetetramine 4-acetamidophenyl 2-boranylacetate–4-acetamidophenol (1/1)], C15H22BN5O3·C8H9NO2. In the first of these molecules, both the borate-ester and acetylamino groups are considerably twisted away from the plane of the intervening benzene ring [dihedral angles = 76.89 (9) and 65.42 (9)°, respectively]. The extended structure of this co-crystal features N—H...O and O—H...O hydrogen bonds, which link the components into (100) sheets and weak C—H...O hydrogen bonds help to consolidate the structure.
“…This resemblance has inspired extensive biological screening of these molecules, and the promising early results led to the syntheses of a large number of ester [96][97][98][99], amide [100,101], peptide [102,103], hydroxamic acid [104], and transition metal [105][106][107] derivatives of amine-carboxyboranes (A-BH 2 COX, X ¼ OR, NR 1 R 2 , or NHOH) containing a broad range substitutes, among other amine-boranes, which have been reviewed recently [2,108,109].…”
Section: Synthesis and Activity Of Amine-carboxyboranes And Their Dermentioning
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