Addition Of Allyltrimethylsilane Research Articles

Polymer-supported (-)-8-phenylmenthyl Auxiliary as an Effective Solidphase Chiral Inductor in the Addition of Nucleophiles to N-acyliminium Ions.

According to our interest in developing new methods for the construction of intricate molecules, a reliable polymer-supported (-)-8-phenylmenthyl chiral auxiliary for the addition of different nucleophiles to chiral-supported N-acyliminium precursors were developed. Merrifield resin was employed to anchor (-)-8-phenylmenthol, which was prepared by nitration of (-)-8-phenylmenthyl chloroacetate followed by reduction of nitro group and subsequent Merrifield resin coupling. Treatment of a suspension of polymer-supported chloroformate and piperidinone in the presence of Et3N resulted in attachment of the substrate onto the solid-support. Treatment of the resulting resin with LiEt3BH/MeOH afforded methoxypiperidine in 87% yield. Then, the addition of allyltrimethylsilane, TMSCN, 2-(trimethylsiloxy)propene and triisopropylsilyloxyfuran and others to the N-acyliminium ion derived from chiral 2- methoxypiperidine carbamate was studied. The stereochemical outcome of the addition of nucleophiles to the supported N-acyliminium ion derived from 2-methoxypiperidine carbamate was proposed through the Si-face, affording after resin cleavage 2-substituted piperidines in 70%-84% yields and selectivities ranging from 4:1-11.1. Moreover, the key intermediates of chiral piperidines have been employed for the synthesis of simple chiral alkaloids such as (R)-pipecolic acid, (R)-pelletierine, (S)-coniine and (R,R)-myrtine. The proposed supported-chiral auxiliary for asymmetric approach may be expected to result not only in efficient solid-phase syntheses of a wide range of alkaloids but also in the development of useful new solid-phase methodologies, particularly for the asymmetric additions to iminium precursors. This work describes the first example of solid-phase synthesis by using supported (-)-8-phenylmenthyl as an effective chiral inductor and would be useful for the synthesis of chiral building block libraries.

ChemInform Abstract: Super-Acid Catalysed Addition of Allylsilanes to Carbonyl Compounds; Synthetic and Mechanistic Aspects.

The addition of allyltrimethylsilane 8 to a variety of aldehydes and one ketone (cyclohexanone) was found to be induced by the super-acid TfOH2+B(OTf)4–(Tf CF3SO2). In contrast to the analogous Lewis acid catalysed reaction, only catalytic amounts (0.5–3 mol%) of the super-acid were required. Modest stereoselectivities were observed with the ‘α-chiral’ aldehydes 15, 21 and 24; in the last two cases, the sense of the selectivity was the opposite of that predicted by ‘chelation control’. Application of the method to the addition of but-2-enyltrimethylsilane 29 to benzaldehyde demonstrated that, unlike the fluoride-catalysed analogue, it is regioselective with respect to allylic inversion. Control experiments employing Me3SiOTf, B(OTf)3 or TfOH as catalysts established that none is sufficiently active to account for the results. Two possible mechanisms are postulated, one in which the activating species is a superacidic proton and one in which it is an ‘Me3Si+’ unit. On the basis of the stereochemical results, it is argued that the latter is marginally more likely.

ChemInform Abstract: The Synthesis of (+)-Nemorensic Acid.

The synthesis of (+)-nemorensic acid in nine steps is described; key steps in the route were the stereoselective Birch reduction of a substituted furan, and addition of allyltrimethylsilane to an oxonium ion at C-5; an X-ray crystal structure of (−)-nemorensic acid provided proof of the relative stereochemistry of the target.

Nonchelated Alkene and Alkyne Complexes of d0 Zirconocene Pentafluorophenyl Cations

This paper describes the generation and properties of nonchelated d(0) zirconocene-aryl-alkene and alkyne adducts that are stabilized by the presence of beta-SiMe(3) substituents on the substrates and the weak nucleophilicity of the -C(6)F(5) ligand. The cationic complexes [(C(5)H(4)R)(2)Zr(C(6)F(5))][B(C(6)F(5))(4)] (4a: R = H, 4b: R = Me) were generated by methide abstraction from (C(5)H(4)R)(2)Zr(C(6)F(5))Me by Ph(3)C(+). NMR studies show that 4a,b contain an o-CF...Zr dative interaction and probably coordinate a PhCl molecule in PhCl solution. Addition of allyltrimethylsilane (ATMS) to 4a,b in C(6)D(5)Cl solution at low temperature produces an equilibrium mixture of (C(5)H(4)R)(2)Zr(C(6)F(5))(H(2)C=CHCH(2)SiMe(3))(+) (7a,b), 4a,b, and free ATMS. Similarly, addition of propargyltrimethylsilane (PTMS) to 4a produces an equilibrium mixture of Cp(2)Zr(C(6)F(5))(HCCCH(2)SiMe(3))(+) (8a), 4a, and free PTMS. The NMR data for 7a,b,and 8a are consistent with highly unsymmetrical substrate coordination and substantial polarization of the substrate multiple bond with significant positive charge buildup at C(int) and negative charge buildup at C(term). PTMS binds to 4a more strongly than ATMS does. The ATMS adducts undergo nondissociative alkene face exchange ("alkene flipping"), i.e., exchange of the (C(5)H(4)R)(2)Zr(C(6)F(5))(+) unit between the two alkene enantiofaces without decomplexation of the alkene, on the NMR time scale.

Allylation of Donor—Acceptor Cyclopropanes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

GaI3 Catalysed Nucleophilic Addition of Allyltrimethylsilane to Aldehydes

In dichloromethane, the nucleophilic addition of allyltrimethylsilane to aldehydes to give the corresponding homoallyl alcohols in good to excellent yields was catalysed effectively by gallium triiodide which was generated in situ by the reaction of gallium metal and iodine.

Allylation of donor--acceptor cyclopropanes.

[reaction: see text] Direct allylation of glycal-derived donor-acceptor cyclopropanes has been achieved with TiCl(4) activation followed by addition of allyltrimethylsilane. The alpha diastereomer is the major product, with selectivities ranging from 3:1 to 10:1 and yields around 80%.

Tandem reactions initiated by the oxidative decarboxylation of 1-benzoyl-2( S)- tert-butyl-6( S)-carboxyperhydropyrimidin-4-one

Treatment of the title perhydropyrimidinone with diacetoxyiodobenzene and iodine followed by addition of allyltrimethylsilane and boron trifluoride etherate afforded 1-benzoyl-2( S)- tert-butyl-2,3-dihydro-4( H)-pyrimidin-4-one in 65–71% yield, via an efficient three-step radical decarboxylation-oxidation-β-elimination tandem reaction. In contrast, when addition of allyltrimethylsilane/BF 3·OEt 2 was suppressed, a remarkable five-step tandem process led to the formation of vinylic iodide, 1-benzoyl-2( S)- tert-butyl-5-iodo-2,3-dihydro-4( H)-pyrimidin-4-one as the main product.

The addition of allyltrimethylsilane to cyclic N-acyliminium ions derived from(S)-(+)-mandelic acid and cyclohexyl-based chiral auxiliaries

The TiCl4- promoted addition of allyltrimethylsilane to chiral 5- and 6-membered N-acyliminium ions employing (S)-(+)-mandelic acid, (1R,2S)-trans-2-phenyl-1-cyclohexanol and (1R,2S,5R)-8-phenylmenthol derivatives as chiral auxiliaries occurred with low to moderate diastereoisomeric ratios (1:1-6:1) to afford 2-substituted amides and carbamates in good yields. The best diastereoselection was observed with (1R,2S,5R)-8-phenylmenthol as the chiral auxiliary. The 2-substituted amides and carbamates were converted to the corresponding alkaloids (S)- and (R)-propyl pyrrolidine and coniine with efficient recovery of the chiral auxiliaries.

Intrinsic gas-phase electrophilic reactivity of cyclic N-alkyl- and N-acyliminium ions.

The intrinsic gas-phase reactivity of cyclic N-alkyl- and N-acyliminium ions toward addition of allyltrimethylsilane (ATMS) has been compared using MS(2) and MS(3) pentaquadrupole mass spectrometric experiments. An order of electrophilic reactivity has been derived and found to agree with orders of overall reactivity in solution. The prototype five-membered ring N-alkyliminium ion 1a and its N-CH(3) analogue 1b, as well as their six-membered ring analogues 1c and 1d, lack N-acyl activation and they are, accordingly, inert toward ATMS addition. The five- and six-membered ring N-acyliminium ions with N-COCH(3) exocycclic groups, 3a and 3b, respectively, are also not very reactive. The N-acyliminium ions 2a and 2c, with s-trans locked endocyclic N-carbonyl groups, are the most reactive followed closely by 3c and 3d with exocyclic (and unlocked) N-CO(2)CH(3) groups. The five-membered ring N-acyliminium ions are more reactive than their six-membered ring analogues, that is: 2a > 2c and 3c > 3d. In contrast with the high reactivity of 2a, its N-CH(3) analogue 2b is inert toward ATMS addition. For the first time, the transient intermediates of a Mannich-type condensation reaction were isolated-the beta-silyl cations formed by ATMS addition to N-acyliminium ions-and their intrinsic gas-phase behavior toward dissociation and reaction with a nucleophile investigated. When collisionally activated, the beta-silyl cations dissociate preferentially by Grob fragmentation, that is, by retro-addition. With pyridine, they react competitively and to variable extents by proton transfer and by trimethylsilylium ion abstraction-the final and key step postulated for alpha-amidoalkylation. Becke3LYP/6-311G(d,p) reaction energetics, charge densities on the electrophilic C-2 site, and AM1 LUMO energies have been used to rationalize the order of intrinsic gas-phase electrophilic reactivity of cyclic iminium and N-acyliminium ions.

The synthesis of (+)-nemorensic acid

The synthesis of (+)-nemorensic acid in nine steps is described; key steps in the route were the stereoselective Birch reduction of a substituted furan, and addition of allyltrimethylsilane to an oxonium ion at C-5; an X-ray crystal structure of (−)-nemorensic acid provided proof of the relative stereochemistry of the target.

Diastereoselective Addition of Allyltrimethylsilane to N-Glyoxyloyl-(2R)-bornane-10,2-sultam. A new synthesis of (S)-1,2-Pentanediol

Addition of allyltrimethylsilane (3) to N-glyoxyloyl-(2R)-bomane:0,2-sultam (4) in the presence of Lewis acid afforded, in high diastereoselecti vity, adduct (2'S)-6 which, after recrystallization, was hydrogenated to give optically pure (S)-1,2-pentanediol (1).

Stereoselective allylsilane additions to α-diketone diketals

Titanium tetrachloride mediated addition of allyltrimethylsilane to α-diketone diketals (cis-1,6-dialkyl-2,5,7,10-tetraoxabicyclo[4.4.0]decanes) leads to 2,3-diallyl-2,3-dialkyl-1,4-dioxanes with very high diastereoselectivity involving an invertive (SN2-like) substitution.

ChemInform Abstract: Catalysis of the Addition of Allyltrimethylsilane to Aldehydes by Silylating Agents. Me3SiB(OTf)4, a New “Supersilylating” Reagent.

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Catalysis of the Addition of Allyltrimethylsilane to Aldehydes by Silylating Agents. Me3SiB(OTf)4, a New, ‘Supersilylating’ Reagent

Catalysis of the Addition of Allyltrimethylsilane to Aldehydes by Silylating Agents. Me₃SiB(OTf)₄, a New, ‘Supersilylating’ Reagent

Super-acid catalysed addition of allylsilanes to carbonyl compounds; synthetic and mechanistic aspects

The addition of allyltrimethylsilane 8 to a variety of aldehydes and one ketone (cyclohexanone) was found to be induced by the super-acid TfOH2+B(OTf)4–(Tf CF3SO2). In contrast to the analogous Lewis acid catalysed reaction, only catalytic amounts (0.5–3 mol%) of the super-acid were required. Modest stereoselectivities were observed with the ‘α-chiral’ aldehydes 15, 21 and 24; in the last two cases, the sense of the selectivity was the opposite of that predicted by ‘chelation control’. Application of the method to the addition of but-2-enyltrimethylsilane 29 to benzaldehyde demonstrated that, unlike the fluoride-catalysed analogue, it is regioselective with respect to allylic inversion. Control experiments employing Me3SiOTf, B(OTf)3 or TfOH as catalysts established that none is sufficiently active to account for the results. Two possible mechanisms are postulated, one in which the activating species is a superacidic proton and one in which it is an ‘Me3Si+’ unit. On the basis of the stereochemical results, it is argued that the latter is marginally more likely.

Diastereoselective asymmetric allylation of chiral α-keto-amides with allyltrimethylsilane. Preparation of protected homoallylic alcohols

In the presence of Lewis acids, protected homoallylic alcohols of high diastereoisomeric excesses (up to 89%) were obtaine by he addition of allyltrimethylsilane to chrial α-keto-amides derived from (S)-proline esters.