Efficient preparations of novel ynamides and allenamides

propargyl derivatives of 4-isopropyl-5,5-diphenyloxazolidin-2-one (DIOZ) are prepared by lithiation of the parent DIOZ (with BuLi in THF) and reaction with the corresponding bromides (Scheme 1). Lithiation in the same solvent, with deprotonation by BuLi on the allylic or propargylic CH 2 group at dry-ice temperature, provides colorful solutions, which are either combined with aldehydes or ketones directly or after addition (with or without warming) of (Me 2 N) 3 TiCl or (i-PrO) 3 TiCl. Conditions have thus been elaborated under which all three types of conjugated lithium compounds react in the g-position with respect to the oxazolidinone N-atom: carbamoyl derivatives of enamines and allenyl amines are formed in yields ranging from 60 to 80% and with diastereoselectivities up to 98% (Schemes 2 ± 5). The CC bond of the N-hydroxyalkenyl groups has (Z)-configuration (products 5 and 8), the allene chirality axis has (M)-configuration (products 9), and the addition to aldehydes and unsymmetrical ketones has taken place preferentially from the Si face. A mechanistic model is proposed that is compatible with the stereochemical outcome (assuming kinetic control and disregarding the presence of Li and Ti species in the reaction mixture; cf. L, M in Fig. 4). Hydrolysis of the enamine derivatives leads to lactols, oxidizable to g-lactones, with recovery of the crystalline oxazolidinone, as demonstrated in three cases (Scheme 6). Thus, the application of chiral oxazolidinone auxiliaries (cf. Figs. 1 and 2) has been extended to the overall enantioselective preparation of homoaldols.

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“…2). These allenes were applied to[4 2] and[4 3] cycloadditions, as well as intramolecular Pauson-Khand reactions[9] [30].…”

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confidence: 99%

Metallations and Reactions with Electrophiles of 4-Isopropyl-5,5-diphenyloxazolidin-2-one (DIOZ) with N-Allyl and N-Propargyl Substituents: Chiral Homoenolate Reagents

Gaul

Seebàch

2002

HCA

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“…The isolated yields for the synthesized N-allenyl analogues shown in table 1 are on par with the benchmark procedure of Hsung, 3 and furthermore, this procedure is experimentally simple. We therefore envisage this 'one-pot' approach being attractive in instances when synthesizing these building blocks on large scale is required.…”

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confidence: 76%

“…2, 3 However, one of the drawbacks of this method is the reliance on the formation and isolation of the propargyl amide (3), which is in turn derived from an amide (1) demonstrated that lactams (7) could be transformed to their N-allenyl analogues (8) using THF/KOH at room temperature.…”

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confidence: 99%

A simple one-pot preparation of N-allenyl amides, ureas, carbamates and sulfonamides using a DMSO/tBuOK protocol

Bousfield

Kimber

2015

Tetrahedron Letters

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“…[5][6][7] We have reported that TBAF can be employed as a base in the anti-elimination reaction of vinyl bromides to obtain the corresponding alkynes. 8,9) The salient feature of this elimination is that dehydrobromination is efficiently brought about by the commercially available hydrated TBAF (TBAF·3H 2 O); further, in contrast to conventional methods, which require strong bases such as t-BuOK, [10][11][12] alkali hydrides, [13][14][15] and alkali metal amides 16,17) as well as strictly anhydrous conditions, our moisture-insensitive protocol is very practical.…”

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confidence: 99%