Allylic Stannanes Research Articles

ChemInform Abstract: Characterization of (Z)-Cyclooct-2-enylstannanes.

(Z)-Cyclooct-2-enyltrimethylstannanes and -triphenylstannanes have been synthesized and characterized by H and C NMR spectra, which indicate a predominating unsymmetrical chair-boat arrangement. A mixture of the cis and trans isomers of both the (4-methylcyclooct-2-enyl)- and (8-methylcyclooct-2-enyl)trimethylstannanes (allylic stannanes) results from a sequence commencing with methylcyanocuprate opening of the monoepoxide of 1,3-cyclooctadiene, which is considered to afford regio- and stereoselectively trans-4-methylcyclooct-2-enol. Chlorination of this alcohol with both thionyl chloride and N-chloro-succinimide/dimethyl sulfide has been conducted and the structures of the chlorides established by NMR methods and use of [1−H]-4-methylcyclooct-2-enol. Trimethylstannylation of the chloride mixtures provides the four possible allylic stannanes, with one of the rearranged 8-methyl isomers slightly predominating. NMR spectra of various fractions from preparative gas chromatography have been obtained, and full assignment of the C NMR spectra of the isomers is reported. Acidolysis of these fractions (with CFCOOD) proceeds rapidly to yield mixtures of H-substituted 3- and 4-methylcyclooctenes, but only one diastereomer of each system appears to be formed, on the basis of the C NMR spectra. This implies that electrophile approach to the π-face at the γ-carbon is not influenced by the orientation of the C-Sn bond but is probably dictated by the predominant molecular conformation.

ChemInform Abstract: Conjugate Addition of Allylic Groups to α,β-Enones via Photoinduced Electron Transfer Reaction of Allylic Stannanes.

Conjugate addition of allylic groups, including allyl and cinnamyl systems, to a variety of α,β-unsaturated ketones could be achieved by photoirradiation with allylic stannanes.

ChemInform Abstract: Stereoselective Total Synthesis of the Pseudopterolide Kallolide A.

A total synthesis of the pseudopterolides, kallolide A (36) and kallolide A acetate (35), has been achieved. The racemic forms were prepared from the syn adduct 20 of furan 13 and stannane 17 (BF(3).OEt(2)-promoted addition) via the 15-membered propargylic allylic ether 25. [2,3]Wittig ring contraction led to the cis, anti, cis product 26. Alcohol 26 was transformed to butenolide 34 with net retention of configuration by Pd(PPh(3))(4)-catalyzed carbonylation of the mesylate 27 and ensuing AgNO(3)-catalyzed cyclization of the derived allenic acid 29. Solvolysis of the SEM ether (at C2) 34 in acetic acid or aqueous t-BuOH afforded racemic kallolide A acetate (35) and kallolide A (36), respectively, with inversion of stereochemistry by an S(N)1 process. Key elements of stereocontrol, including the steric outcome of the [2,3]Wittig ring contraction, the allenic ester isomerization, and the solvolysis reactions, were predicted from molecular mechanics calculations. The C8 and C2 epimers 45 and 46 of the cis, anti, cis kallolide A SEM ether precursor 34 were also prepared. The synthetic route originated from the anti adduct 19 of aldehyde 13 and the allylic chloride 16 and CuCl (cat), HSiCl(3), and i-Pr(2)NEt. Adduct 19 was subjected to the same sequence as the syn counterpart 20 to produce the trans, anti, cis [2,3]Wittig ring contraction product 42. The derived allenoate 44 afforded a 1:1 mixture of butenolides 45 and 46 upon sequential treatment with TBAF and AgNO(3). Finally, the natural enantiomer (+)-36 of kallolide A was synthesized from the enantioenriched syn adduct (+)-20, prepared by addition of allylic stannane 17 to aldehyde 13 promoted by a modified chiral acyloxyborane Lewis acid.

ChemInform Abstract: Aldehyde Addition to Allylic Stannanes via a Transmetalation Pathway: Stereocontrol in the Absence of Internal Coordination.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Diastereoselective Allylstannane Additions to (S)-5,6-Dihydro-2H-5-phenyloxazin-2-one. A Concise Synthesis of (S)-β-Methylisoleucine

The addition of allyl stannanes to (S)-4,5-dihydro-5-phenyl-2H-oxazinone (3) was achieved under Brønsted acid catalysis to give 2-allylmorpholinones with high diastereoselectivity (up to dr 14.2:1). The product of dimethylallyltributylstannane addition to 3 was converted to l-beta-methylisoleucine, an alpha-amino acid residue found in the complex, biologically active marine-derived peptides polytheonamides A and B, and polydiscamides A-C.

Asymmetric Conjugate Addition of Crotylstannane: Synthesis of (-)-Lasiol

Lasiol, the major component of the mandibular gland secretion, serves as the primary sex attractant of the male ant, Lasius meridionalis. Our interest in lasiol stems from the stereochemistry of the chiral methyl substituents and the synthetic challenges posed by this common structural motif. As such, an asymmetric 1,4-conjugate addition of an allylic stannane to produce the 1,2-anti-dimethyl arrangement with high stereocontrol has resulted in the synthesis of (-)-lasiol.

Enantiospecific Synthesis and Allylation of All‐Carbon‐Substituted α‐Chiral Allylic Stannanes

Once difficult to obtain, the title compounds can be prepared in virtually enantiomerically pure form with a bis(triorganostannyl) zinc reagent (see scheme). Subsequent diastereoselective thermal (left) and Lewis acid promoted reactions (right) illustrate the synthetic potential of these compounds.

Palladium-mediated reductive coupling, a stereoselective approach to the 8-dehydropumiliotoxin skeleton

Reductive cyclisation of an E-vinyl bromide with an allylic acetate proceeds under palladium catalysis to give the 8-dehydropumiliotoxin skeleton, a potential advanced precursor to 8-deoxypumiliotoxin alkaloids. Control of the stereochemistry of the E-vinyl bromide precursor is achieved readily using the Kogen or Bruckner bromophosphonate reagents and the reductive cyclisation proceeds with retention of the vinyl bromide stereochemistry. The mechanism for the cyclisation involves an in situ conversion of the allylic acetate to an allyl stannane followed by an intramolecular Stille-type coupling.

Isolation and Characterization of a Nucleophilic Allylic Indium Reagent

Transmetalation between allylic stannanes and indium halides gave allylic indium dihalides. The bond length of In−C is 2.172 Å, which is close to the reported average indium−carbon bond length. The isolated allylic indium dibromide with two phthalan ligands showed nucleophilicity for a carbonyl compound.

P′CP′-Pincer palladium complex-catalyzed allylation of N,N-dimethylsulfamoyl-protected aldimines

The P′CP′-pincer palladium complex-catalyzed allylation of N, N-dimethylsulfamoyl-protected aldimines with allyl(tributyl)stannane is investigated for the preparation of N-homoallylic sulfamides. The desired N, N-dimethylsulfamoyl-protected products are obtained in moderate to high yields in DMF under very mild conditions and a high yielding and convenient deprotection of the N, N-dimethylsulfamoyl group is also demonstrated.

ChemInform Abstract: Conjugate Addition of Allyl Stannanes with Concomitant Triflation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Distannylations and Silastannylations of In Situ Generated Allenes

Owing to their high versatility, organometallic compounds have become extremely valuable building blocks and have found a wide range of applications in organic synthesis, especially in modern cross-coupling chemistry. This development has been possible through the tremendous progress over the past 40 years in the synthesis and applicability of organometallic substrates. Besides the typically used monometalated compounds, also dimetalated derivatives are of enormous interest, especially if different organometallic centers can made to undergo reactions selectively. In this context, Mitchell et al. reported on palladiumcatalyzed distannylations and silastannylations of alkynes and allenes. The catalytic dimetalation of allenes has the advantage that products are formed that have a vinylic and an allylic metal group as well. Both functionalities can be coupled independently and selectively, which makes the products of the catalytic dimetalation of allenes highly valuable building blocks for organic synthesis. Besides diborations, the addition of stannagermanes and silaboranes to alkenes and alkynes have been reported as well. Disilylations of allenes are also possible, but in general this reaction requires higher reaction temperatures. In the last few years, Cheng et al. have reported on palladium-catalyzed carbostannylations, carbosilylations, and acyl metalations. Our group has also been involved for several years in hydroand distannylations of alkynes and allenes, especially in the presence of molybdenum and tungsten catalysts. Depending on the catalyst used, propargyl acetateA can selectively be converted either into the vinyl stannane B or the dimetalated allyl acetate C (Scheme 1). The molybdenum-catalyzed hydrostannylation of allenyl alcohols D provided allyl stannanes E in good yields. Herein we present a new protocol towards dimetalated alkenes starting from alkynes or vinyl stannanes. This reaction came into our focus during our investigations of the influence of different catalysts on the regioselectivity of hydrostannylations. While Bu3SnH addition towards the alkyne 1a gave rise to the expected vinyl stannane 2a in the presence of the molybdenum catalyst [Mo(CO)3(CNtBu)3] (MoBI3), the palladium-catalyzed reaction surprisingly provided the distannylated product 3a (Scheme 2). At the beginning it was unclear how this product could be formed, but we speculated that also the palladium-catalyzed reaction provided 2a as an intermediate, which might undergo elimination to an allene under the reaction conditions. Therefore, we investigated the

Conjugate Addition of Allyl Stannanes with Concomitant Triflation

A new method for the conjugate addition of allyltributylstannane with concomitant triflation is described. This reaction works with functionalized enones, enals, enoates, and vinylogous esters. The resulting vinyl triflates can be used for intramolecular Heck reactions to afford the products of 5-exo-trig cyclization.

Synthesis and Catalytic Application of Chiral 1,1′‐Bi‐2‐naphthol‐ and Biphenanthrol‐Based Pincer Complexes: Selective Allylation of Sulfonimines with Allyl Stannane and Allyl Trifluoroborate.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis and Catalytic Application of Chiral 1,1‘-Bi-2-naphthol- and Biphenanthrol-Based Pincer Complexes: Selective Allylation of Sulfonimines with Allyl Stannane and Allyl Trifluoroborate

New easily accessible 1,1'-bi-2-naphthol- (BINOL-) and biphenanthrol-based chiral pincer complex catalysts were prepared for selective (up to 85% enantiomeric excess) allylation of sulfonimines. The chiral pincer complexes were prepared by a flexible modular approach allowing an efficient tuning of the selectivity of the catalysts. By employment of the different enantiomeric forms of the catalysts, both enantiomers of the homoallylic amines could be selectively obtained. Both allyl stannanes and allyl trifluoroborates can be employed as allyl sources in the reactions. The biphenanthrol-based complexes gave higher selectivity than the substituted BINOL-based analogues, probably because of the well-shaped chiral pocket generated by employment of the biphenanthrol complexes. The enantioselective allylation of sulfonimines presented in this study has important implications for the mechanism given for the pincer complex-catalyzed allylation reactions, confirming that this process takes place without involvement of palladium(0) species.

A diastereoselective carbocyclisation of allene-hydrazones through the intramolecular allylic transfer reaction

A diastereoselective synthesis of cyclic hydrazines was achieved from a carbocyclisation of allene-hydrazones by the Pd-catalyzed distannylation of an allene moiety, followed by the transmetallation of allylic stannane intermediates with TiCl4.

Insertion of CO2into a palladiumallyl bond and a Pd(ii) catalysed carboxylation of allyl stannanes

The complex 2,6-bis[(di-t-butylphosphino)methyl]phenyl allyl palladium (PCP(tBu)Pd-allyl, 3) reacts with CO(2) in a very fast insertion reaction to give the corresponding butenoate complex. The reaction is thought to occur via a cyclic six-membered transition state (7), where the gamma-carbon of the allyl group is linked up with the CO(2)-carbon. A group of related PCP complexes were investigated as catalysts for the carboxylation of tributyl(allyl)stannane. A catalytic cycle is proposed for this reaction where the rate determining step is the transmetallation between tin and palladium. The carboxylation reaction is faster using less sterically crowded catalysts whereas the electron richness of the palladium complexes seems less important for reactivity. Thus, there was no apparent difference in reactivity between 2,6-bis[(di-phenylphosphino)methyl]phenyl palladium triflouroacetate (13) and resorcinolbis(diphenyl)phosphinite palladium triflouroacetate (10). Both of these complexes give high turnovers for the carboxylation of tributyl(allyl)stannane (80% in 16 h using a ca. 5% catalyst loading and 4 atm CO(2) pressure). On the other hand complex 3 was inactive in the catalytic carboxylation reaction.

First Example of an Enantiospecific sp3—sp2 Stille Coupling of a Chiral Allylstannane with Aryl Halides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Palladium/Lewis Acid Catalyzed Desymmetrization of Fulvene-Derived Bicyclic Hydrazines: A Facile Synthesis of Substituted Alkylidene Cyclopentenes

Desymmetrization of fulvene-derived bicyclic hydrazines by a palladium/Lewis acid catalyzed reaction with allyl and vinyl stannanes leading to the efficient synthesis of synthetically important alkylidene cyclopentenes is described.

Synthetic Study of Azaspiracid-1: Synthesis of the EFGHI-Ring Fragment

Here, we report a synthesis of the lower half C21-C40 fragment of the shellfish toxin, azaspiracid-1. The C28-C40 fragment was synthesized by a coupling between the C28-C35 epoxide and the C36-C40 dithioacetal anion, followed by the HI-ring spiroaminal formation. An aldehyde corresponding to the C28-C40 fragment was then coupled with the C21-C27 allylic stannane by using InCl3. Finally, the FG-ring was constructed by HF.pyridine to accomplish the synthesis of the suitably protected C21-C40 fragment.