Enantioselective Alkynylation of Aldehydes Catalyzed by [2.2]Paracyclophane-Based Ligands

Abstract

[reaction: see text] [2.2]Paracyclophane-based ketimine ligands were evaluated as catalysts for the enantioselective addition of in situ-prepared alkynylzinc reagents to aldehydes. The initial high activity and enantioselectivity of these ligands could be improved by an additive screening. The final protocol gives chiral propargyl alcohols in up to >98% ee.

Planar‐ and Central‐Chiral N,O‐[2.2]Paracyclophane Ligands: Non‐Linear‐Like Effects and Activity

“…[10 -13] Within the last few years, various new paracyclophane ligands have been used for asymmetric catalysis. [14 -17] In particular, the asymmetric 1,2-addition reaction of zinc reagents [18] such as alkyl, [19 -21] alkenyl, [22] aryl [23] and alkynyl [24] zinc reagents with aldehydes or imines, [19,20,23] can be efficiently controlled by the application of hydroxy[2.2]paracyclophane ketimine ligands.[17]We recently reported the synthesis of the [2.2]paracyclophane-based ketimine ligands (R P ,S)-2, (S P ,S)-2, (R P ,S)-3, and (S P ,S)-3 and their application in asymmetric catalysis such as the addition of zinc reagents to aldehydes. [19] During these studies, we observed not only that these ligands are highly active, [21,25] but also that they display mismatched and matched cases.…”

Solvent-free Synthesis of Propargylic Alcohols using ZnO as a New and Reusable Catalyst by Direct Addition of Alkynes to Aldehydes

“…38 As it is shown in Table 2, entries 15-18, less reactive alkylacetylenes (much less acidic than 2a) were also applicable to the alkynylation of an aldehydes in good yields. In particular, alkynes 2b-e underwent the addition reaction with isobutyraldehyde 1a to furnish the corresponding propargylic alcohols in 60-65% yields (entries [16][17][18], which is a costeffective process for the preparation of new compounds. As indicated above, solvent or base totally interrupted this alkynylation reaction, in this case to show the ability of ZnO as a good catalyst we apply this method to a solid alkyne and aldyhydes.…”

Enantioselective addition of phenylacetylene to aldehydes catalyzed by polymer‐supported titanium(IV) complexes of β‐hydroxy amides

“…[2][3][4][5][6][7][8][9][10][11] Since the first efficient asymmetric alkynes addition to aldehydes was demonstrated by Soai 12 using (1S,2R)-N,N-dibutylnorephedrine, many chiral ligands, such as N-methylephedrine, [13][14][15] BINOL and its derivatives, 5,10,[16][17][18][19][20][21] and sulfonamides 22,23 have been used successfully in this reaction. Other chiral ligands, such as amino alcohols, 24,25 oxazoline, [26][27] and imino alcohol, 28 have also been reported to catalyze this reaction.…”