Beiträge zur Chemie des Bors, 202. Borylierung von Aminosäuren mit einem Amino‐imino‐boran

Abstract

Contributions to the Chemistry of Boron, 2021). – Borylation of Amino Acids by an Amino‐imino‐borane Reactions of (tert‐butylimino)(2,2,6,6‐tetramethylpiperidino)‐borane (3) with amino acid esters or N,N‐dimethyl amino acids lead to the N‐borylated products 5 and boryl esters 11, respectively. Amino acids and 3 yield the O,N‐bis‐boryl compounds 13 and/or 1,3,2‐oxazaborolidin‐5‐ones 14, depending on the size of the organyl substituent R at the α‐carbon atom of the amino acid. Increasing the bulk of this group favours the formation of 14 with elimination of tert‐butylamine. The five‐membered OBNCC ring of 14 is planar according to an X‐ray structure analysis of 14e. (2,6‐Diisopropylphenylimino)(2,2,6,6‐tetramethylpiperidino)borane reacts with amino acids similar to 3, but tetramethylpiperidine is eliminated on ring formation to produce 20. N‐Monoalkyl amino acids and 3 predominantly give oxazaborolidin‐5‐ones.

Reaction of 2,3-Dihydro-1H-1,3,2-diazaboroles and Diphenylketene: A Novel Synthesis of 1,3,2-Oxazaborolidines

“…In 2b (X = F), 2c (X = NH 2 ), and 2d (X = NMe 2 ), where the boron atoms are linked to π-donating groups X the 11 B NMR resonances (δ 22.3−25.2) are deshielded by only δ 2.0−3.1 on going from 1 to 2 . For comparison 1,3,2-oxazaborolidin-5-ones derived from α-amino acids and an amino-iminoborane display 11 B resonances at δ 27.0−27.4 . In the remaining products 2a (X = Br, δ 26.0), 2e (X = Me, δ 34.5), 2f (X = SnMe 3 , δ 38.2), and 2g (X = alkenyl, δ 30.9) a more pronounced deshielding (Δδ 8.3−12.4) of the boron nuclei relative to the corresponding 1,3,2-diazaborole precursors is observed.…”

“…A series of 1,3,2-oxazaborolidin-5-ones were obtained by the borylation of ( S )-alanine, ( S )-valine, ( S )-leucine, ( S )-isoleucine, and ( S , R )- tert -leucine with ( tert -butylimino)-(2,2,6,6-tetramethylpiperidino)borane . Amino acid derived oxazaborolidin-5-ones are excellent catalysts for highly enantioselective Diels−Alder reactions, − the Mukaiyama aldol reaction of aldehydes and silyl enol ethers, , and asymmetric aldol reactions of silyl ketene acetals. , …”

Beiträge zur Chemie des Bors, 208 Reaktionen eines Amino‐imino‐borans mit Phosphin‐, Phosphon‐ und Phosphorsäuren

“…Die Umsetzungen liefern gemaD G1. (1) Umsetzungen der Phosphonsauren RP(0)(OH)2 (R = CH3, C6H5) mit 1 fuhren ebenfalls zur Bildung von Produkten mit tetrakoordiniertem Bor neben den isolierten Verbindungen vom Typ 4. Auch bei Variation der Versuchsbedingungen lieDen sich mono-0-borierte Phosphonsauren 5 weder gewinnen noch nachweisen.…”

Novel boracycles from 2-amino-2-methylpropan-1-ol and borane methyl sulfide: Synthesis and X-ray crystal structures

“…Nö th also determined the structure of the prolinol derived oxazaborolidine dimer 4, and referred to those structures as ''abnormal dimers'' [11]. Nö th also reported the preparation of trigonal boron atoms in an oxazaborolidine ring using (tert-butylimino)(2,2,6,6-tetramethylpiperidino)-borane and amino acid as reactants (Scheme 2) [12].…”