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February 2017
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21 Reads
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2 Citations
Heteroaryllithiums, obtained via MesLi mediated halogen- lithium exchange, undergo intramolecular addition onto acrylamide and acrylate moieties. Both electron rich (thiophenyl) and electron deficient (pyridinyl, quinolinyl) heteroaromatic halides can be used for the formation of six- and seven membered rings, providing an efficient route to fused indolizines and pyrroloazepines in moderate to good yields
August 2016
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13 Reads
ChemInform
Different 2-alkenyl-substituted pyrroles and pyrrolidines are investigated as cyclization precursors: Pd sources, ligands (chiral and achiral), bases and solvents are tested to produce an optimal result concerning the required stereocenters.
April 2016
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19 Reads
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9 Citations
The generation of quaternary and tertiary stereocentres at C-10 of the pyrroloisoquinoline skeleton through intramolecular Mizoroki-Heck reactions of 2-alkenyl-substituted pyrroles and pyrrolidines has been studied. The cyclizations proceeded in moderate to good yields (up to 81 %), but with low enantioselectivity when chiral phosphanes such as (R)-BINAP were used as ligands. However, enantiomerically pure 10-substituted pyrrolo[1,2-b]isoquinolines were efficiently obtained by a diastereoselective approach using chiral nonracemic pyrrolidines as substrates, generating a tertiary stereocentre.
December 2015
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71 Reads
The diastereoselective Mizoroki-Heck reaction of N-benzylpyrrolidines that incorporate a protected allylic alcohol moiety allows the synthesis of enantiomerically pure pyrrolo[1,2-b]isoquinolines, generating a tertiary stereocenter. The best results were obtained with the use of bulky phosphanes, as P(o-Tol)3. When a good leaving group, such as pivaloyl is used as a protecting group, the trans-10-vinyl substituted pyrroloisoquinoline (10S,10aS)-2a is obtained as the major diastereoisomer in moderate yield. On the other hand, when the allylic alcohol is protected as a silyl ether, the protected alcohol is retained, obtaining an enol ether, whichafter deprotection and reduction leads to the trans-10-hydroxymethyl substituted pyrrolisoquinoline (10S,10aS)-5, in enantiomerically pure form, with complete diastereoselectivity.
December 2015
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45 Reads
Mizoroki-Heck reaction constitutes an effective method for the formation of quaternary stereocenters. This reaction has been applied to functionalized 2-alkenylpyrroles as substrates in which the b-elimination is blocked by a methyl substituent. 10,10-Disubstituted pyrrolo[1,2-b]isoquinolines can be obtained using different palladium catalysts and chiral bidentate phosphanes as ligands, although with low enantioselectivities. In some cases, competition between Mizoroki-Heck reaction and C-H direct arylation reaction on the pyrrole nucleus has also been observed for this type of polyfunctionalized substrates. Finally, we have shown that quaternary stereocenters can be generated using chiral phosphane ligands as (R)-BINAP, through a cascade polyene cyclization.This procedure has been successfully applied to the construction of tetracyclic framework of Lycorine class of Amaryllidaceae alkaloids
... N-substituted vinyl-substituted pyrrole-2-carbaldehydes 140 were obtained by Wittig reaction in good overall yields (Scheme 47). [49,50] Then compounds 140 under the action of mesithyllithium (MesLi) at low temperature were converted into 8-substituted thienoindolizine 141. ...
February 2017
... The synthetic methods for the preparation of pyrrolo[2,1a]isoquinolines are mainly based on two strategies: annulation of the pyrrole ring to the isoquinoline moiety or annulation of the isoquinoline core to the pyrrole or lactam cycle. When the formation of the pyrrolo[2,1-a]isoquinoline moiety proceeds via annulation on the pyrrole core, it is necessary to use palladium-catalyzed reactions, in particular the Mizoroki-Heck coupling reaction [19,20]. For N-alkylated pyrroles, the intramolecular Heck reaction using Pd(PPh 3 ) 4 as a catalyst with sodium acetate as a base or Pd(PPh 3 ) 2 Cl 2 and Ph 3 P as a catalyst with potassium carbonate as a base allows to obtain pyrroloisoquinolines with good yields [21,22]. ...
April 2016
