全氟烷基磺酰溴与杂原子取代烯键的反应

全氟烷基磺酰溴与杂原子取代烯烃, 如溴乙烯, 乙酸乙烯酯, 三甲基硅乙烯加成, 得相应的加成物, 与烯醇硅醚反应, 水解后得到α位溴代酮和全氟烷基亚磺酸. 全氟磺酰氯与1-三甲基硅氧基-1-叔丁基乙烯在紫外光照下反应, 生成α位全氟烷基化的酮. 全氟烷基磺酰溴溴化苯酚和甲氧基苯, 得到对位溴化产物. α,α-二氯三氟乙基亚磺酸钠与溴水在20-25℃反应, 得α,α-二氯三氟乙基磺酰溴, 其化学反应性与全氟烷基磺酰溴类似, 但稳定性较差.     

Tris(trimethylsilyl)silyl-governed aldehyde cross-aldol cascade reaction

The use of the tris(trimethylsilyl)silyl (TTMSS) group in aldehyde-derived silyl enol ethers affords aldehyde cross-aldol products with high yields and allows for unprecedented reactivity. The reaction is catalyzed by 0.05 mol % of HNTf2, and can easily be managed to give beta,delta-bis-, beta,delta,gamma-tris-, and beta,delta,zeta-tris-hydroxy-aldehydes with extremely high selectivity by simple stoichiometric control. High diastereoselectivity is obtained in all cases, and the use of chiral aldehydes affords Felkin products when there are nonchelating substituents, chelation products when there is a chelating sbustituent, and syn products when there is beta-substitution. HNTf2 is proposed to be an initiator, and highly Lewis acidic TTMSSNTf2 is the true catalyst.     

Synthese de nouveaux derives silicies cycliques fonctionnels

Methyl or trimethylsilyl ether derivatives of mono- or di-phenols easily undergo disilylation to give disilylated enol ethers or bis(enoxysilanes) with a 1,4-cyclohexadienic ring which are new classes of intermediates in synthesis. In the case of monophenol derivatives hydrolysis affords stable δ-silyl-β,γ-unsaturated ketones, which are converted to the corresponding conjugated cyclohexenones by desilylation (e.g. 4-allyl-2-cyclohexenone which was previously difficult to prepare). In the case of diphenol derivatives cyclohexanediones are obtained upon hydrolysis. Polysilylation occurs with methyl phenyl thio ether, pyrocatechol and even with o-cresol derivatives, to give new products.     

Organocatalytic Michael addition of aldehydes to a β-silylmethylene malonate to form intermediates for the enantioselective synthesis of hydroxylated valerolactones and piperidines

The direct Michael addition of enolizable aldehydes to dimethyl(phenyl)silylmethylene malonate was catalysed by an (S)-diphenylprolinol trimethylsilyl ether/acetic acid combination. The adducts were formed in good yield, high diastereoselectivity and excellent enantioselectivity. Chiral valerolactone and piperidine skeletons embedded with a silyl and other functionalities have been made out of the adducts. A total synthesis (+)-simplactone B has been achieved from one of the adducts.     

N-heterocyclic carbene-catalyzed Mukaiyama aldol reactions

N-Heterocyclic carbenes were shown to be highly effective catalysts to promote Mukaiyama aldol reactions. In the presence of only 0.5 mol % of N-heterocyclic carbene (5), various aldehydes and 2,2,2-trifluoroacetophenone underwent Mukaiyama aldol reactions in THF with trimethylsilyl ketene acetal (2) at 23 degrees C as well as with trimethylsilyl enol ether (7) at 0 degrees C to afford aldol adducts in good yields. These conditions are extremely mild and operationally simple and tolerate various functional groups. [reaction: see text]     

Diastereoselective synthesis of cis-fused pyrano and furanobenzopyrans catalyzed by indium trichloride or triphenyl phosphonium perchlorate

Indium trichloride (InCl₃) and triphenyl phosphonium perchlorate (TPP) are found to be effective catalysts for the cyclization of o-hydroxyaldimines with 3,4-dihydro-2H-pyran and 2,3-dihydrofuran at ambient temperature to afford novel pyrano and furanobenzopyran derivatives in excellent yields with high diastereoselectivity. One pot syntheses of pyrano and furanobenzopyrans from o-hydroxybenzaldehyde, aromatic amines and an enol ether under identical conditions is reported for the first time. Similarly, o-hydroxyaldimine reacted with ethyl vinyl ether to give 2-ethoxy-4-N-aryl aminobenzopyran in good yields.     

Lewis base catalyzed Mannich-type reactions between trimethylsilyl enol ethers and aldimines

Lewis base catalyzed Mannich-type reaction between trimethylsilyl enol ethers and N-tosylaldimines is described. Nitrogen anions generated from amides or imides such as lithium benzamide or potassium phthalimide are found to be effective Lewis base catalysts in DMF at room temperature to afford the corresponding beta-amino carbonyl compounds in good to high yields; the oxygen anion generated from carboxylic acids such as lithium acetate was also found to be effective in dry DMF. The above-mentioned lithium acetate-catalyzed Mannich-type reaction between aldimines and various trimethylsilyl (TMS) enol ethers such as silyl ketene acetal proceeded smoothly even in water-containing DMF. Then, Lewis base catalyzed three-component Mannich-type reactions of TMS enol ether, tosylamide, and aromatic aldehyde having electron-withdrawing group such as p-nitrobenzaldehyde were investigated. The reaction proceeded smoothly to afford the corresponding beta-amino ester in good yield. Further, ammonium carboxylates such as tetrabutyl ammonium acetate or tetrabutyl ammonium benzoate were found to be more effective Lewis base catalysts in the above-mentioned Mannich-type reaction. The synthesis proceeded in various solvents at lower temperatures. The reaction between aldimines and TMS enol ethers generated from thioester and various ketones such as propiophenone or cyclohexanone also proceeded smoothly to afford the corresponding beta-amino carbonyl compounds in high yields with good to high anti-selectivities.     

Diastereoselective Prins-type reaction of cycloalkenylcyclopropanol silyl ethers and alpha,beta-unsaturated aldehyde acetals

Electrophilic addition of 1-(1-cyclohexenyl)-1-cyclopropanol trimethylsilyl ether to alpha,beta-unsaturated aldehyde acetals under Lewis acidic conditions proceeds with good to excellent diastereoselectivity to afford spirocyclobutanones containing three contiguous stereocenters. A convenient entry to enantioselective syntheses is available by use of a nonracemic C2-symmetric acetal. Elaboration of the resulting adducts provides ready access to medium-sized carbocycles.     

Influence of the beta-alkoxy group on the diastereoselectivity of Aldol reactions of tetrahydro-4H-thiopyran-4-one with 4-Alkoxytetrahydro-2H-thiopyran-3-carboxaldehydes

The diastereoselectivity of the aldol reaction of tetrahydro-4H-thiopyran-4-one (3) with 1,4-dioxa-8-thiaspiro[4.5]decane-6-carboxaldehyde (9a) under a variety of conditions is examined. Under optimized conditions, three of the four possible diastereomers from this aldol reaction can be obtained selectively (3-16:1). Reactions of 9a with the Li, B, Mg(II), and Ti(IV) enolates of 3 and with the corresponding trimethylsilyl enol ether 4b in the presence of BF(3) x OEt(2), SnCl(4), or TiCl(4) as promoters gave the Felkin adducts exclusively (>95%) as mixtures of syn (11a) and anti (12a) diastereomers. Use of the "amine-free" Li enolate of 3 gave 12a with a much higher diastereoselectivity (9:1) and yield (70%) than that obtained using the lithium diisopropylamide-generated Li enolate of 3 (2-3:1; 15-40%). The TiCl(4)-promoted reaction of 4b with 9a gave 11a with excellent selectivity (16:1). In contrast, the MgBr(2) x OEt(2)-promoted reaction of 4b with 9a gave the anti-Felkin adducts exclusively as a 3:1 mixture of syn (13a)/anti (14a) diastereomers. Similar aldol reactions of 3 with the cis and trans isomers of 4-(methoxy)methoxytetrahydro-2H-thiopyran-3-carboxaldehyde (9b and 9c) were examined to probe the influence of the ketal protecting group in 9a on the observed aldol diastereoselectivity. The results are rationalized by applying Evans' stereochemical model for merged 1,2- and 1,3-asymmetric induction (non-chelation), with the exception of the MgBr(2) x OEt(2)-promoted reactions of 4b with 9a, 9b, and 9c, which are accommodated by assuming chelation control. Comparison of the reactions of 9a, 9b, and 9c suggests that the ketal group in 9a uniquely allows high levels of either Felkin or anti-Felkin selectivity to be achieved.     

A novel route to the marasmane skeleton via a tandem rearrangement-cyclopropanation reaction. total synthesis of (+)-isovelleral

A general and efficient route to the marasmane skeleton is described. Total syntheses of two simple marasmanes (35 and 37) in racemic form were achieved using a MgI2-catalyzed rearrangement-cyclopropanation reaction of trimethylsilyl enol ether 31 derived from naphthalenone 30. The reaction proceeds in high yield with complete diastereoselectivity and does not require the use of special cyclopropanation reagents. Application of this novel route to the marasmane framework was extended to the synthesis of naturally occurring (+)-isovelleral (41).     

The reactions of perfluoroalkanesulfonyl bromide with hetero-atom substituted olefinic bonds

Perfluoroalkanesulfonyl bromides reacted with vinyl bromide, vinyl acetate and trimethyl vinyl silane to give the corresponding adducts with the evolution of SO₂. Perfluoroalkanesulfonyl bromide reacted with trimethyl silyl enol ether followed by hydrolysis to give the corresponding α-bromoketones and perfluoroalkanesulfinic acid. However, perfluoroalkanesulfonyl chlorides reacted with trimethyl silyl enol ether of pinacolone on UV irradiation to give the corresponding α-perfluoroalkyl derivatives of pinacolone. Under mild condition, perfluoroalkanesulfonyl bromide also brominated phenol and anisole to give the corresponding p-bromo derivatives. Sodium α, α-dichlorotrifluoroethanesulfinate reacted with bromine in water at 25°C to form α, α-dichlorotrifluoroethanesulfonyl bromide which was thermally less stable than but similar in reactivity to perfluoroalkanesulfonyl bromide.     

Remarkable tris(trimethylsilyl)silyl group for diastereoselective [2 + 2] cyclizations

[reaction: see text] Diastereoselective [2 + 2] cyclizations of aldehyde- and ketone-derived silyl enol ethers with acrylates is described. The use of the tris(trimethylsilyl)silyl group allows for unprecedented reactivity, yields, and selectivity for these cyclizations. The presence of silicon-silicon bonds proved to be important for this transformation, where typical silyl groups (TBS and TIPS) failed to give any desired product. The bulky bis(2,6-diphenylphenoxide) aluminum triflimide catalyst was essential for high diastereoselectivity.     

Controlled rearrangement of lactam-tethered allenols with brominating reagents: a combined experimental and theoretical study on α- versus β-keto lactam formation

N-Bromosuccinimide (NBS) smoothly promotes the ring expansion of lactam-tethered allenols to efficiently afford cyclic α- or β-ketoamides with good yields and high chemo-, regio-, and diastereoselectivity, through controlled C-C bond cleavage of the β- or γ-lactam nucleus. Interestingly, in contrast to the rearrangement reactions of 2-azetidinone-tethered allenols, which lead to the corresponding tetramic acid derivatives (β-keto lactam adducts) as the sole products, the reactions of 2-indolinone-tethered allenols under similar conditions give quinoline-2,3-diones (α-keto lactam adducts) as the exclusive or major products. To rationalize the experimental observations, theoretical studies have been performed.     

Theoretical Analysis of the Heterocyclic [4+2] Cycloaddition Between Pyridinium Ion and Enol Ether

Dearomative heterocyclic [4+2] cycloaddition between the N-(2,4-dinitrophenyl)pyridinium ion of nicotinamide and an enol ether was analyzed by Density Functional Theory (DFT) calculations. The calculation revealed that the reaction undergoes stepwise bond formation rather than occurring in a concerted manner. The experimental products were found to be both kinetically and thermodynamically favored. The calculated transition states and intermediate suggested that the high diastereoselectivity is derived from the electrostatic interaction between the 2-nitro group of the pyridinium ion and the hydrogen of the enol ether.     

Cyclooctanone synthesis via a formal [6+2] cycloaddition reaction of a dicobalt acetylene complex

An efficient formal [6+2] cycloaddition reaction of a new six-carbon unit with enol silyl ether was developed on the basis of a dicobalt hexacarbonyl propargyl cation species. Under the influence of EtAlCl₂, 6-benzoyloxy-2-(triisopropylsilyloxy)-1-hexen-4-yne-dicobalthexacarbonyl reacted with enol triisopropylsilyl ethers to yield 7-(triisopropylsilyloxy)-3-cyclooctyn-1-one-dicobalthexacarbonyl derivatives in good yield. The reactions with cyclic enol silyl ethers as well as acyclic enol silyl ethers exhibited remarkably high diastereoselectivity.     

New approaches toward the synthesis of (D-homo) steroid skeletons using Mukaiyama reactions

New, short, and flexible procedures have been developed for syntheses of steroid and D-homo steroid skeletons. A Mukaiyama reaction between the silyl enol ether of 6-methoxytetralone and 2-methyl-2-cyclopentenone or carvone, with transfer of the silyl group to the receiving enone, gave a second silyl enol ether. Addition of a carbocation, generated under Lewis acid conditions from 3-methoxy-2-butenol, 3-ethoxy-3-phenyl-2-propenol or 3-methoxy-2-propenol to this second silyl enol ether gave adducts, which could not be cyclized by aldol condensation to (D-homo) steroid skeletons. The Mukaiyama-Michael reaction of the silyl enol ether of 6-methoxy tetralone with 2-methyl-2-cylopentenone gave a second silyl enol ether, which reacted in high yield with a carbocation generated from 3-hydroxy-3-(4-methoxyphenyl)propene. Ozonolysis of the double bond in this adduct gave a tricarbonyl compound (Zieglers triketone), which has been used before in the synthesis of 9,11-dehydroestrone methyl ether. A second synthesis of C17 substituted CD-trans coupled (D-homo) steroid skeletons has been developed via addition of a carbocation, generated with ZnBr₂ from a Torgov reagent, to a silyl enol ether containing ring D precursor. The obtained seco steroids have been cyclized under formation of the 8-14 bond by treatment with acid. The double bonds in one of the cyclized products have been reduced to a C17-substituted all trans steroid skeleton.     

Regio- and stereodefined synthesis of trimethylsilyl enol ethers resulted from the isomerization of α-trimethylsilyl ketones

The isomerization of an α-trimethylsilyl ketone is lead to the corresponding trimethylsilyl enol ether with the enhanced regioselectivity by heating or by the assist of trimethylsilyl trifluoromethanesulfonate. The thermal reaction discloses a new regiodefined (E)-selective route to silyl enol ethers.     

A Novel Concept for Combinatorial Chemistry in Solution: Synthesis of Highly Substituted Pyrrolidines by Multicomponent Domino Reactions

The multicomponent domino Knoevenagel hetero‐Diels? Alder hydrogenation process of N‐[(benzyloxy)carbonyl(Cbz)‐protected amino aldehydes with N,N‐dimethylbarbituric acid and the trimethylsilyl enol ethers 1 – 3 leads to the formation of the substituted pyrrolidines 12 – 15 . Under the same conditions, reaction of the trimethylsilyl enol ether 4 , obtained from acetophenone, gave the primary amines 18a , b probably due to a hydrogenolytic cleavage of the intermediately formed pyrrolidines. The zwitterionic products were obtained in high purity simply by precipitation with Et₂O.     

General route to 2,4,5-trisubstituted piperidines from enantiopure beta-amino esters. Total synthesis of pseudodistomin B triacetate and pseudodistomin F

The Michael addition reaction of enantiopure beta-amino esters with methyl acrylate followed by Dieckmann condensation and enol silylation affords the enol ethers 6, which are hydrogenated with catalysis by Raney-Ni at 80 atm and 80 degrees C to provide 2,4, 5-trisubstituted piperidines with high diastereoselectivity. In this case Ni-H attacks the C-C double bond from the direction of the 2-alkyl group to provide the products in which 2,4,5-trisubstrited groups are all cis to each other. While hydrogenation of enol ether 13 without a N-Boc protecting group gives the product 15 in which the 4-hydroxy group and 5-ester moiety are trans to the 2-alkyl group. By using the diastereoselective hydrogenation products 9d and 9e as key intermediates, pseudodistomin B triacetate and pseudodistomin F are synthesized. The key steps for these transformations include Curtius rearrangement and Julia olefination.     

REACTIONS OF β-KETO SULFOXIDES WITH SULFUR ELECTROPHILES. PART II. STEREOCHEMICAL AND CONFIGURATIONAL STUDIES OF THE INTERMEDIATE ENOLATES

Abstract

Some β-keto sulfoxides containing different groups at the sulfinyl moiety were submitted to sulfenylation reaction employing two procedures: in homogeneous media and by PTC to give the corresponding monosulfenylated products. The Z configuration for the enolates of the β-keto sulfoxides independently of the group at the sulfur moiety is proved by ¹H NMR NOE difference experiments. The diastereoselectivity observed in the case of a t-butyl sulfinyl derivative is rationalized by preferred attack of the sulfur electrophile to the unhindered face of enolate not shielded by t-butyl group, as shown by X-ray analysis of the corresponding enol ether.