Stereoselective synthesis of allylic amines by the reaction of titanium-alkyne complexes with imines

Gao, Yuan; Harada, K.; Sato, Fumie

doi:10.1016/0040-4039(95)01140-d

Cited by 23 publications

(23 citation statements)

References 23 publications

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“…[29] Most of the selectivities we have observed, however, differ sharply from those reported for reactions with aldehydes, ketones and imines. [9,30] For instance, the reactions of the complex derived from 1-trimethylsilyloct-1-yne with these compounds display higher and opposite regioselectivities to those found in our reaction of the same complex with carbon dioxide (Table 2, Entry 7). [9,30] This observation could be due in part to the small size of carbon dioxide, making it less sensitive to steric effects, and also possibly to differences in the reaction mechanisms.…”

Section: Selectivity Issuesmentioning

confidence: 60%

Titanium‐Mediated Carboxylation of Alkynes With Carbon Dioxide

Six

2003

Eur J Org Chem

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The regioselective carboxylation of nonactivated internal alkynes can be performed with carbon dioxide under atmospheric pressure using a simple procedure based on the chemistry of Sato‐type diisopropyloxytitanacyclopropenes. Various polysubstituted vinylcarboxylic acids and butenolides can be prepared in this way. In addition, this paper describes an experimental protocol for the preparation of solutions of (η2‐cyclopentene)diisopropyloxytitanium. This complex also reacts with carbon dioxide, and mediates pinacol coupling of acetophenone. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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Section: Selectivity Issuesmentioning

confidence: 60%

Titanium‐Mediated Carboxylation of Alkynes With Carbon Dioxide

Six

2003

Eur J Org Chem

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“…23 In contrast to the reaction with aldehydes, the reaction of the silylacetylene-titanium complex proceeds with almost complete regioselectivity. 23 In contrast to the reaction with aldehydes, the reaction of the silylacetylene-titanium complex proceeds with almost complete regioselectivity.…”

Section: Equation 17mentioning

confidence: 99%

Synthetic Reactions Mediated by a Ti(O-i-Pr) / 2i-PrMgX Reagent

2000

Synlett

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A new titanium complex (η 2 -propene)Ti(O-i-Pr) 2 (1), generated in situ by treatment of Ti (O-i-Pr) 4 with 2 equiv of i-PrMgX (X = Cl or Br), nicely acts as a versatile titanium(II) equivalent to effect the following unique transformations. Thus, alkynes react with 1 to afford the alkyne-titanium complexes of type (η 2alkyne)Ti(O-i-Pr) 2 , which could be utilized as a vicinal vinylic dianion equivalent in the reactions with various kinds of electrophiles. Allyl-and allenyltitaniums could readily be prepared from allylic or propargylic alcohol derivatives by the reaction with 1 through an oxidative addition pathway. While acetylenic esters resulted in an intramolecular nucleophilic acyl substitution (INAS) reaction to afford α,β-unsaturated carbonyl compounds, olefinic esters undergo tandem INAS and intramolecular carbonyl addition reactions to give cyclopropanols. Ene-ene, ene-yne, and yne-yne coupling reactions proceed in an intra-or intermolecular way via a cyclometallation reaction, and the generated titanacyclic complexes react with a variety of electrophiles in a chemo-, regio-, stereoselective way. This account describes these reactions and their utilization in organic synthesis which include representative applications to asymmetric synthesis and natural product synthesis. Inter-and Intramolecular Coupling of Olefin and Acetylenes 6Conclusion

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“…Interestingly, entry 4 (Table 1) demonstrated a complete reversal in regioselectivity with respect to known cross-coupling reactions of TMSsubstituted alkynes and imines (C À C bond formation typically occurred b to the TMS substitutent), hence demonstrating that the directing effect of the tethered alkoxide completely overrides the directing effect of the TMS substituent. [10] With this site-selective alkyne-imine cross-coupling reaction in hand, we focused our attention on developing an intermolecular aza-Pauson-Khand-like annulation reaction for the synthesis of tetrasubstituted g-lactams (Table 2).…”

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confidence: 99%

An Alkoxide‐Directed Intermolecular [2+2+1] Annulation: A Three‐Component Coupling Reaction for the Synthesis of Tetrasubstituted α,β‐Unsaturated γ‐Lactams

2007

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Metal-mediated [2+2+1] annulations are a powerful class of reactions for the synthesis of functionalized five-membered rings.[1] These processes, which proceed by the initial formation of a metallacyclopentene followed by the insertion of CO, have been described for a variety of functionalized p systems (alkyne-alkene, [2] alkyne-ketone, alkene-ketone, [3] alkene-aldehyde, [3,4] and alkyne-imine [5] ), and have been useful for the preparation of functionalized carbocyclic and heterocyclic molecules. The vast majority of these annulation reactions are synthetically useful only in intramolecular contexts, whereby geometrical constraints imposed by a tether between the two reacting p systems dictate the siteselectivity in the C À C bond-forming event. The corresponding bimolecular coupling reaction of unsymmetrically substituted p systems from metal-mediated [2+2+1] annulations has proven much less general as a result of the challenges associated with the control of both reactivity and regioselectivity in the generation of the polysubstituted metallacyclopentene (Scheme 1, 1+2![A-D]!3-6). Here, we describe a highly regioselective process for the bimolecular [2+2+1] annulation that provides a convenient and direct route to tetrasubstituted a,b-unsaturated g-lactams.Nitrogen-containing heterocycles are ubiquitous structural motifs in natural products and small molecules of biomedical relevance. Many methods for the convergent assembly of such structures target CÀC or CÀN bond formation by nucleophilic addition to C=N-based p systems, condensation, or metal-mediated cross-coupling reactions. [6] An alternative and potentially more powerful pathway to functionalized heterocycles is through multicomponent coupling reactions between all-carbon-based p systems, imines, and CO 2 by using [2+2+1] annulation reactions.[5] To date, these annulation processes have been of limited utility in organic synthesis because of the poor levels of regioselection commonly observed in the initial cross-coupling reaction between the internal alkyne and the imine (alkyne+imine! azametallacyclopentene). [7] A general means to control the site-and stereoselective C À C bond formation in these bimolecular coupling reactions would render such processes versatile for the synthesis of highly functionalized nitrogencontaining acyclic and heterocyclic targets. Our recent success in the development of selective cross-coupling reactions of unactivated and differentially functionalized p systems (alkyne-alkyne [8] and alkyne-alkene [9] ), in which the unique reactivity of Group IV metal alkoxides was harnessed, led us to question whether we could define such a process for alkyne-imine cross-coupling reactions through the directed carbometalation of an internal alkyne with an azametallacyclopropane.Our initial results for the regioselective cross-coupling reaction between internal alkynes and imines are shown in Table 1. In short, preformation of an azametallacyclopropane (imine, Ti(OiPr) 4 , and cyclopentylmagnesium chloride, À78 to À40 8C) was foll...

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Stereoselective synthesis of allylic amines by the reaction of titanium-alkyne complexes with imines

Cited by 23 publications

References 23 publications

Titanium‐Mediated Carboxylation of Alkynes With Carbon Dioxide

Titanium‐Mediated Carboxylation of Alkynes With Carbon Dioxide

Synthetic Reactions Mediated by a Ti(O-i-Pr) / 2i-PrMgX Reagent

An Alkoxide‐Directed Intermolecular [2+2+1] Annulation: A Three‐Component Coupling Reaction for the Synthesis of Tetrasubstituted α,β‐Unsaturated γ‐Lactams

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