Allenylmethylsilanes as Nucleophiles in N-Acyliminium Ion Chemistry

Abstract

Treatment of a variety of N-acyliminium ion precursors with 2,3-butadienyl(trimethyl)silane and related allenes in the presence of BF(3).OEt(2) provides good yields of N-protected 2-(aminomethyl)-substituted 1,3-dienes, which prove to be useful substrates for subsequent Diels-Alder and alkene metathesis reactions. [reaction: see text]

Synthesis of a Naturally Occurring Diene‐Containing Amino Acid and Its Glutamyl Dipeptide via N‐Acyliminium Ion Chemistry

“…Treatment of 14 with acidic methanol gave the more stable N-acyliminium ion precursor 15 in 63 % yield over two steps (Scheme 3). Coupling of allene 6 [14,16] with 15 was performed in acetonitrile at 0°C, using BF 3 ·OEt 2 as the Lewis acid providing the desired α-diene amino acid 16 in 87 % yield.…”

“…To a stirred solution of 21 (1.50 g, 6.07 mmol) and allenyltrimethylsilane [14,16] (1.53 g, 1.21 mmol) in CH 2 Cl 2 (30 mL) at -78°C was added slowly BF 3 ·OEt 2 (1.53 mL, 1.21 mmol). The resulting yellow reaction mixture was warmed slowly to -20°C, carefully monitored by TLC (PE/EtOAc, 2:1).…”

“…[12,13] We envisioned that these tetradehydro-isoleucine (tdIle) derivatives could be prepared using a method developed earlier in our group, using allenylmethylsilane 6 as a nucleophile in a reaction with a glycine derived N-acyliminium ion 5 (Scheme 1). [14] In this article we report the first total syntheses of 1a and 1b employing this strategy. In addition we detail the enzymatic resolution of the diene amino acid 1a.…”

Effects of Silyl Substituents on the Palladium‐Catalyzed Asymmetric Synthesis of Axially Chiral (Allenylmethyl)silanes and Their SE2′ Chirality Transfer Reactions

“…[5] Indeed, examples of transferring the allenic axial chirality onto a stereogenic carbon atom which is derived from the incoming intermolecular reactant have been extremely rare. [6][7][8] Recently, we developed a Pd-catalyzed reaction for the preparation of various multisubstituted allenes, [9a-9h] and the use of an appropriate chiral Pd catalyst enables axially chiral allenes of high enantiopurity to be furnished. [7,9i-9l] The reaction was applied to the asymmetric synthesis of axially chiral (allenylmethyl)silanes 3 (Scheme 1), and the obtained enantiomerically enriched 3 were applied in the S E 2Ј reaction to produce diene derivatives 5 containing a stereogenic carbon atom.…”

“…[7] The second step of this sequence was a rare example of the intermolecular axis-tocenter chirality transfer reaction. [6][7][8] Although the reaction selectivity of the asymmetric allene synthesis and the subsequent S E 2Ј chirality transfer reaction were studied. It was found that as the steric bulk of the silyl groups in the 3-bromo-5-silylpenta-1,3-dienes was increased from -SiMe 3 to -SiiPr 3 , the enantioselectivity of the two enantioselective processes also improved.…”