Ene-type Reaction Research Articles

Asymmetric catalysis of ene-type reaction with fluoral by chiral titanium complex: A semi-empirical and ab-initio analysis of ene reactivity

The chiral titanium complex-catalyzed ene-type reaction with fluoral is shown to serve as an efficient route for the asymmetric synthesis of CF 3-substituted compounds of biological and synthetic importance in extremely high enantiomeric excesses (>95% ee). The ene reactivity of trihaloacetaldehyde including fluoral is estimated in terms of the balance of LUMO energy level vs. electron density on the carbonyl carbon.

Alkylation of dimethylaminobis(trifluoromethyl)borane by 1-alkenes

Dimethylaminobis(trifluoromethyl)borane, (CF 3) 2BNMe 2 ( A), undergoes B-alkylation on treatment with 1-alkenes of the general formula (R 1CH 2)(R 2)CCH 2 to yield triorganoboron adducts Me 2(H)NB(CF 3) 2CH 2(R 2)CCHR 1(R 1 H, R 2Me ( I); R 1H, R 2  CH 2(CF 3) 2BNHMe 2 ( II); R 1Me, R 2 Et ( III); R 1H, R 2CH 2( tBu) ( IV); R 1H, R 2Ph ( V); R 1H, R 2 CHCMe 2 ( VI); R 1Ph, R 2H ( VII); R 1 nPr, R 2H ( VIII); R 1 iPr, R 2H ( IX)). In contrast, monosubstituted ethene derivatives (R 2)CHCH 2(R sBu, Ph, Mes, Me 3Si, Et 3Si) react with A to form the corresponding methylmethyleneimine boron adducts H 2CN(Me)B(CF 3) 2CH 2C H 2R 2 ( X, XII–XV). With ( tBu)(Me)CCH 2, A undergoes both types of reaction, yielding a 1/4 mixture of Me 2(H)NB(CF 3) 2CH 2 ( tBu)CCH 2 ( XIa) and H 2CN(Me)B(CF 3) 2CH 2CH(Me)( tBu) ( XIb). Whereas I–IX and XIa are formed by an ene-type reaction, X and XIb–XV result from a shift of a hydride from the dimethylamino group to the alkylating substituent. The novel boranes have been characterized by elemental analysis and multinuclear NMR, IR and mass spectroscopy.

BC bond formation by ene-type reactions of dimethylaminobis(trifluoromethyl)borane with nitriles and carbonyl compounds. Crystal structure of (NCCH 2)(CF 3) 2B · NHMe 2

Dimethylaminobis(trifluoromethyl)borane, (CF 3) 2BNMe 2 ( A), reacts with nitriles RCH 2CN | to yield triorganoboron adducts | NCCHR)(CF 3) 2B · NHMe 2 (R  H ( I), Cl ( II), Me ( III) and Et ( IV)). Analogously carbonyl compounds of the general formula R 2C(O)CH 2R 1 form the respective complexes (R 2C(O)CHR 1)(CF 3) 2B · NHMe 2: R 1  H, R 2  tBu ( V), R 1  H, R 2  Ph ( VI), R 1  H, R 2  CCHCHC(Me)O ( VII), R 1  H, R 2  Me ( VIII), R 1  H, R 2  CHCMe 2 ( IX), R 1  H, R 2  OMe ( X), R 1  H, R 2  O tBu ( XI), R 1  H, R 2  OSiMe 3 ( XII), R 1  H, R 2  OC(Me)CH 2 ( XIII), R 1  H, R 2  OCH 2CHCH 2 ( XIV), R 1  H, R 2  O tBu ( XI), R 1  OSiMe 3 ( XII), R 1  H, R 2  OC(Me)CH 2 ( XIII), R 1  H, R 2  OCH 2CH CH 2 ( XIV), R 1  H, R 2  NMe 2 ( XV), R 1  H, R 2  NEt 2 ( XVII), R 1  Cl,R 2  OEt ( XVIII), R 1  Me, R 2  OMe ( XIX), R 1  Et, R 2  OMe ( XX), R 1  C(O)OMe, R 2  OMe ( XXI), R 1  C(O)O tBu, R 2  O tBu ( XXII), R 1, R 2  CH 2OCH 2 ( XXIII). Their identities have been confirmed by multinuclear NMR, IR, and mass spectroscopy. The crystal and molecular structure of I has been determined by an X-ray diffraction study. Individual molecules are linked to form infinite chains through hydrogen bonding. The BC (1.627(3) Å (BCF 3) and 1.629(4) Å (BCH 2CN)) and BN bond lengths (1.600(3) Å are normal.

Preparation of benzo[b]thiophenes by Pd(0)-catalyzed intramolecular cyclization of allyl (and propargyl) o-iodophenyl sulfides.

Benzo[b]thiophenes are prepared by intramolecular Pd(0)-catalyzed Heck reaction of allyl o-iodophenyl sulfides. Pd(0)-Catalyzed intramolecular cyclization of o-iodophenyl propargyl sulfide in the presence of a hydride donor gives 3-methylene-2,3-dihydrobenzo[b]thiophene, which reacts with several enophiles in ene type reactions. However, allyl (and propargyl) aryl sulfides react with palladium(II) chloride to afford polymeric [PdCl(SAr)] 2.

Ene-type reaction of trisubstituted monoterpene alkenes with methyl sulfite and thionyl chloride

Trisubstituted methylalkenes react with methyl sulfite at ∼25°C in the presence of BF3 · Et2O in the ene-type fashion to give the corresponding methallyl sulfinates. Such compounds can also be prepared under considerably milder conditions by the Et2AlCl-catalyzed reaction of thionyl chloride with mono- and dienes followed by methanolysis of intermediate alkyl sulfinyl chlorides. These reactions represent a new method for terminal functionalization of linear isoprenoids.

Intermolecular oxonium–ene reaction: a new entry to stereocontrolled synthesis of tetrahydropyrans

The intermolecular ene-type reaction with a lactol-derived oxonium ion intermediate as an enophile is shown to exhibit a high level of diastereofacial selectivity to afford predominantly the 2,6-trans-tetrahydropyrans in spite of the diastereoisomeric ratio of the starting δ-lactol derivatives.

Further investigation on the reaction of heterocyclic ketene aminals with ethyl propiolate: ene-type reaction of enamines and an unusual substituent effect

The reaction between heterocyclic ketene aminals and ethyl propiolate 1 has been investigated and an unusual substituent effect observed. Although 2-(benzoylmethylene)-1, 3-dimethylimidazolidines 2 failed to add to 1, 2-(benzoylmethylene)imidazolidine 3 reacted with it to give the fused heterocycle 5via the intermediate 4. With one methylated nitrogen, the heterocyclic ketene aminals 6 or 7 reacted with 1 to afford the heterocyclic compounds 9 or 10 and ethoxycarbonylvinyl substituted heterocycles 11 or 12. By controlling the reaction conditions, 9 or 10 and 11 or 12 can be synthesized selectively. The results are interpreted in terms of an ene-addition mechanism with steric interaction in the intermediates. A correlation between reactivity and intramolecular hydrogen bonding is also discussed.

Electrophilic ene-type reactions of phenyl vinyl sulfoxide with alkenes

Phenyl vinyl sulfoxide 1 can be made to react as an α,β-dicarbocation with alkenes by formation of one, or two new C–C bonds. These reactions take place at or below room temperature, under the conditions of the Pummerer reaction, i.e. trifluoroacetic acid and its anhydride. The key step is an electrophilic ene-type reaction between a thionium ion and the alkene. The primary β-trifluoroacetoxy sulfides thus formed then undergo rearrangement via an episulfonium ion to the more stable, secondary isomer.

Convenient synthesis of isoprenoid chlorides by a direct chlorination process

A direct and easy chlorination of substituted isoprenoid derivatives in a hydrocarbon solvent affords allylic chlorides via an ene-type reaction. These mild conditions tolerate various functional groups and this procedure is very convenient for an industrial process.

An Ene-type Reaction of Thionyl Chloride with Linear Isoprenoids

A diethylaluminium chloride-catalysed ene-type reaction of thionyl chloride with citronellyl, geranyl and linalyl acetates, followed by treatment of the reaction mixture with methanol, leads smoothly to the corresponding allylic methyl sulfinates.

Photo-oxygenation of Styrenic Estrogens: Structural Analysis of 8,9-Didehydro-, 6,7-Didehydro-, and 9,11-Didehydroestrone Derivatives and Their Reactivity towards Singlet Oxygen

A series of didehydro-3-O-methyl-estrones having a styrenic framework, with the ring-A-conjugated double bond in all three possible positions (8,9-didehydro- (6),9,11-didehydro- (1b), 6,7-didehydro- (9), and the 12,18-di-nor-8,9-didehydroestrone analog 11), were compared for their reactivity towards singlet oxygen. Under dye-sensitized photo-oxygenation conditions, both, products derived from ene-type reactions with the isolation of a stable hydroperoxide and a fragmentation product, were obtained from 6 (see Scheme 3), while only fragmentation took place for 1b (Scheme 1), Kinetic studies indicated that 6 is more reactive towards 1O2 than 1b (β = 9.2·10−3 mol·1−1 vs 3.3·10−2 mol·1−1, resp.). The observed reactivity, apparently, does not match with ene-type reaction and [2 + 2]cycloaddition being in competition, since the most activated substrate 6 preferentially yields ene-type products and their derivatives. Conformational analysis on the structure of 6 and 1b, both calculated by molecular-mechanic techniques (MMPMI) and determined by X-ray diffraction, show that the allylic H-atoms satisfy the orthogonality rule for ene-type reactions. The product distribution is best rationalized by applying Fukui's rule which takes into account a combination of electronic and geometric factors. Substrates 9 and 11 yielded photo-products arising from ene-type reaction with no stable primary products isolated (Scheme 4). Geometric considerations based on the calculated structures by molecular mechanics are consistent with the observed results.

Organic heterocyclothiazenes. Part 15. Pyrazolotrithiadiazepines and their rearrangement to 1,2,3-dithiazoles

Treatment of 6-bromotrithiadiazepine 1 with Hunig's base in the presence of diphenyldiazomethane 2a gives the hetaryne cycloadduct 3a. Neat thermolysis of this at 210 °C results in very rapid loss of N2 and ‘HNS’ in a deep-seated rearrangement to give the new indeno-1,2,3-dithiazole ring system 4a. A mechanism proposed for this rearrangement (Schemes 2 and 5) is supported by the isolation of a key intermediate 12 when the cycloadduct 3a is thermolysed in dilute solution at lower temperatures. The intermediate 12 dimerises reversibly to give 13, possibly by a 8-electron ene-type reaction. Other diaryldiazomethanes 2 give analogous hetaryne cycloadducts 3(70–80%) which rearrange similarly when heated to give more complex 1,2,3-dithiazoles 4(20–40%)(Scheme 1).

An ene-type reaction between an unactivated olefin and an ?activated? sulfoxide, and some properties of the resulting sulfonium salts

1. Using DMSO and MeSOPh it has been shown for the first time that O-trifluoroacetylated sulfoxides react with unactivated trisubstituted olefins to give allylsulfonium salts. 2. LiClO4 has been found to accelerate this ene-type reaction. 3. It has been found for the first time in the aliphatic series that the competition between [3, 2]-rearrangement and the Stevens rearrangement of the S-ylid generated from the allylsulfonium salt is governed by the type of counterion present, and this observation has been rationalized.

The Stereochemistry of Organometallic Compounds. XXXIII. Preparation and Reactions of Some Substituted Buta-1,3-Dienes

Hydroformylation and hydrocyanation of 2-methylhex-1-en-3-yne surprisingly both involve addition to the alkyne leading to the formation of formyl- and cyano-buta-1,3-dienes whose reactivity in Diels-Alder and ene-type reactions has been investigated.

Ene-type reaction of “activated sulfoxide” with non-activated olefin. Counter-ion dependent (1,2)- [formula omitted]. [3,2] shift dichotomy of ylides derived from allylsulfonium salts

Lithium perchlorate-accelerated ene-type reaction of an “activated sulfoxide” with non-activated trisubstituted olefin to give respective allylsulfonium salt and counter-ion dependent (1,2) - vs . [3,2] rearrangement of the ylide generated from this salt are discussed.

ChemInform Abstract: Selective Preparation of Hydroperoxides in Photosensitized Oxygenation

This article reviews the current research interest in the selective preparation of hydroperoxides in photosensitized oxygenation.This involves two sections; (i) selective formation of allylic hydroperoxides by ene type reaction of olefins with singlet oxygen and (ii) stereospecific preparation of α-hydroperoxysulfide with singlet oxygen oxidation of thiazolidine derivatives.

Intramolecular ene-type reaction between a diene–Fe(CO)3complex and alkene units

Heating of allylic amide or allylic ester substituted diene–Fe(CO)3 complexes such as (7) and (10)(140 °C) results in an intramolecular coupling of the pendant double bond with the diene moiety to give spirolactam and spirolactone derivatives; the stereochemical course of this reaction was established by an X-ray crystal structure determination of the lactone derivative (11).

Synthesis of (.+-.)-endo- and (.+-.)-exo-brevicomin via ene reaction of the Pummerer rearrangement product derived from 4-chlorophenyl methyl sulfoxide.

(±) -endo- (4) and (±) -exo-Brevicomin (5) were synthesized by employing the ene-type reaction of 4-chlorophenylthiomethyl trifluoroacetate (2) as the key step. The ene product 7 was converted, via two steps, into the ketosulfone 9, whose epoxidation followed by acid hydrolysis afforded the cyclic acetal as a mixture, 12a and 12b (89 : 11). Recrystallization of the mixture followed by desulfurization yielded (±) -endo-brevicomin (4). On the other hand, successive treatment of 9 with osmium tetroxide, hydrochloric acid, and Raney nickel afforded a mixture of (±) -exo- (5) and (±) -endo-brevicomin (4) (89 : 11).

光増感酸素化反応による選択的ヒドロペルオキシドの合成

This article reviews the current research interest in the selective preparation of hydroperoxides in photosensitized oxygenation.This involves two sections; (i) selective formation of allylic hydroperoxides by ene type reaction of olefins with singlet oxygen and (ii) stereospecific preparation of α-hydroperoxysulfide with singlet oxygen oxidation of thiazolidine derivatives.

The Reaction of Silyl Enol Ethers With Ethyl Azodicarboxylate and 4-Phenyl-1,2,4-Triazoline-3,5-Dione

Abstract The ene-type reaction between silyl enol ethers and azodiesters yields α-keto 4-phenyl 1,2,4 triazolidine-3,5-dione in the case of 1,2,4-triazoline-3,5-dione. and α-keto dicarbo-ethoxyhydrazides in the case of diethyl azodicarboxylate. These reactions proceed in qcod yield and offer potential routes to α-nitrogen substituted ketones.