Synthesis of α‐Propargylglycinates Using the Borono‐Mannich Reaction with Pinacol Allenylboronate and Potassium Allenyltrifluoroborate

Abstract

The three component borono‐Mannich reactions of ethyl glyoxylate, primary or secondary amines and pinacol allenylboronate or potassium allenyltrifluoroborate are highly regioselective and give α‐propargylglycinates. The (S)‐N‐tert‐butylsulfinyl imine of ethyl glyoxylate underwent an indium chloride catalyzed addition reaction with allenyl potassium trifluoroborate in a highly regioselective and diastereoselective manner to give ethyl (S)‐α‐propargylglycinate after N‐deprotection in 97 % ee.

Catalytic asymmetric propargyl- and allylboration of hydrazonoesters: a metal-free approach to sterically encumbered chiral α-amino acid derivatives

“…Subsequently, an In-catalyzed variant of this reaction was reported. 8 Recently, Pyne and co-workers 9 demonstrated that N-tert-butylsulfinyl imines undergo In-catalyzed couplings with allenylboron species (Fig. 1b).…”

Synthesis and Reactivity of Allenylboron Compounds

“…The regioselectivity was generally excellent except for the reaction with primary amines. Pyne's group resolved this problem (Scheme 18c) [65] by introducing ethyl glycinate as an electrophile, which can not form a boronate intermediate through B−O coordination of the carboxylate group. However, this borono‐Mannich reaction only worked with the primary amine as a substrate.…”

Allenylation and Propargylation Reactions of Ketones, Aldehydes, Imines, and Iminium Ions Using Organoboronates and Related Derivatives

“…Reactive intermediates related to 44 and 50 (involving boron coordination to the CO 2 of the glyoxylic acid) may be also be involved. In a shorter study the Pyne group 35 found that the reaction of glyoxylic acid (monohydrate), pinacol allenylboronate 3, and dibenzylamine gave the corresponding α-allenylglycine of 54 (R 1 = R 2 = Bn) while the reaction using diphenylmethylamine, rather than dibenzylamine, gave a 27:73 mixture of propargyl and allenyl products, respectively.…”

“…The Pyne group 35 demonstrated that the borono-Mannich reactions of ethyl glyoxylate, primary or secondary amines, and pinacol allenylboronate 3 or potassium allenyltrifluoroborate (10) were highly regioselective and gave ethyl α-propargylglycinates 56 (Scheme 36). These results are different to those found using glyoxylic acid and allenylboronic acid 8, supporting the mechanisms shown in Scheme 37.…”

“…The Pyne group 35 The Javo group extended these studies to reactions of cyclic N-sulfonyl ketimines 76 and 78 (Scheme 45). 41 Under similar conditions to those used in Scheme 43 propargylated products 77 and 79, respectively, were obtained often in high yields and in high enantiomeric purities (90-98% ee).…”