210642-61-8Relevant academic research and scientific papers
Use of Silylated Formiates as Hydrosilane Equivalents
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Paragraph 0514, (2021/09/26)
The present invention relates to a method for preparing organic compounds of formula (I) by reaction between a silylated formiate of formula (II) and an organic compound in the presence of a catalyst and optionally of an additive. The invention also relates to use of the method for preparing organic compounds of formula (I) for the preparation of reagents for fine chemistry and for heavy chemistry, as well as in the production of vitamins, pharmaceutical products, adhesives, acrylic fibres, synthetic leathers, and pesticides.
Catalytic asymmetric synthesis of quaternary carbon centers. Exploratory studies of intramolecular Heck reactions of (Z)-α,β-unsaturated anilides and mechanistic investigations of asymmetric Heck reactions proceeding via neutral intermediates
Ashimori, Atsuyuki,Bachand, Benoit,Calter, Michael A.,Govek, Steven P.,Overman, Larry E.,Poon, Daniel J.
, p. 6488 - 6499 (2007/10/03)
Intramolecular Heck reactions of seven (Z)-α,β-unsaturated 2-iodoanilides catalyzed by Pd-BINAP were surveyed using two reaction conditions: (1) silver-promoted cyclizations in the presence of 2 equiv of Ag3PO4 and (2)base-promoted cyclizations in the presence of 4 equiv of 1,2,2,6,6-pentamethylpiperidine (PMP). A comparison of these results with the outcome of the corresponding intramolecular Heck reactions of the E stereoisomers leads to the following conclusions: (1) (E)- and (Z)-α,β-unsaturated 2-iodoanilides give opposite enantiomers of the Heck product when Ag3PO4 is the HI acceptor (cationic pathway); the absolute configuration of the product is independent of alkene geometry when the HI acceptor is PMP (neutral pathway). (2) When the 2-substituent is Me or prim-alkyl, stereoinduction is optimal in PMP-promoted insertions of Z substrates which occur with ee's as high as 97%. (3) When the 2-substituent is large, stereoinduction is optimal in insertions of E substrates carried out in the presence of Ag3PO4. (4) Contributions from the β-alkene substituent are minor. The neutral Heck reaction manifold can be entered from triflate substrates by carrying out the cyclization in the presence of added halide salts. The ability to vary both the alkene geometry and the Heck reaction pathway allows chiral 3,3-disubstituted-2-oxindoles having a wide range of substituents at the quaternary carbon (Me, prim-alkyl, tert-alkyl, and aryl) to be prepared with useful levels of enantioselection (72-97% ee). A number of studies were carried out aimed at clarifying the mechanism of the neutral Heck reaction pathway. Key results are the following: (1) Chiral amplification studies show that the catalyst is monomeric Pd-BINAP. (2) Investigations of monophosphine analogues of BINAP, which were designed to mimic a partially dissociated BINAP chelate, support the conclusion that BINAP is chelated during the enantioselective step. (3) Enantioselectivity is insensitive to solvent polarity. From these data, we propose that the stereochemistry determining step of the neutral pathway occurs during the process in which iodide is displaced by the tethered alkene (Figure 2, 41 → 47 → 45). In light of the variety of pentacoordinate intermediates that could be involved, it is premature to advance a model to rationalize stereoinduction in asymmetric Heck reactions proceeding by the neutral pathway. Nonetheless, the finding that the enantioselective step of asymmetric Heck reactions taking place by the neutral pathway involves five-coordinate intermediates significantly broadens the vista for design of asymmetric ligands for this and related reactions.
