Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones via Their Hexacarbonyldicobalt Complexes. A New Use of Alkyne−Co<sub>2</sub>(CO)<sub>6</sub> Complexes in Organic Synthesis

Iwasawa, Nobuharu; Matsuo, Tetsuji; Iwamoto, Mutsuo; Ikeno, Taketo

doi:10.1021/ja9734004

Cited by 74 publications

(31 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Treating 1‐alkynyl cyclopropanol 116 with stoichiometric quantities of cobalt delivers cyclopentenone 117 (Scheme a). Later, by adding a triarylphosphite ligand to the reaction, the cobalt loading could be reduced to 5–10 mol‐% without affecting product yields . Trost and co‐workers have shown that a ruthenium catalyst is also competent in this reaction …”

Section: Homoenolates As Nucleophilic Reagentsmentioning

confidence: 99%

Modern Developments in the Chemistry of Homoenolates

Mills

Rousseaux

2018

Eur J Org Chem

View full text Add to dashboard Cite

Homoenolates are unique synthetic intermediates which display umpolung reactivity. Homoenolates and homoenolate equivalents like cyclopropanols have seen a recent surge in popularity due to their particular utility for accessing β‐functionalized carbonyl derivatives. This popularity has been enabled by the development of protocols for facile access to cyclopropanols and homoenolates from a variety of readily available starting materials. This microreview will highlight common strategies for generating cyclopropanols and metal homoenolates, as well as procedures for homoenolate functionalization, with a particular emphasis on protocols that have appeared after 2003. As an amphoteric molecule, two main reactivity modes have been established: the homoenolate reacts as a carbon nucleophile for β‐functionalization reactions and/or as a carbonyl electrophile, a strategy which has only emerged in the past few years. This microreview will highlight the use of homoenolates as convenient intermediates for accessing especially challenging motifs. The use of homoenolate chemistry in the context of natural product and pharmaceutical synthesis will also be presented.

show abstract

Section: Homoenolates As Nucleophilic Reagentsmentioning

confidence: 99%

Modern Developments in the Chemistry of Homoenolates

Mills

Rousseaux

2018

Eur J Org Chem

View full text Add to dashboard Cite

show abstract

“…Comparison of the coupling constants with known data15 and additional NOE experiments confirmed that the hydrogen atoms are trans-positioned in compound 10 and cis-positioned in compound 11.…”

mentioning

confidence: 60%

Diastereoselective Friedel-Crafts Alkylation Reactions Employing Chiral Cation Precursors with Polar α-Substituents

Stadler¹,

Mühlthau²,

Rubenbauer³

et al. 2006

Synlett

View full text Add to dashboard Cite

Precursors 5-7 of chiral para-methoxybenzyl cations (2-4), which carry a polar substituent (NO 2 , CN, OH) at the stereogenic a-carbon atom, reacted under acidic conditions with high facial diastereoselectivity (dr = 75:25 to >95:5) to the corresponding 1,1-diarylalkanes threo-9 (50-87% yield). Catalytic amounts of Sc(OTf) 3 as Lewis acid were sufficient to convert epoxide 7 into the corresponding alcohols threo-9ca and threo-9cb.Friedel-Crafts alkylations belong to the most important C-C bond-formation reactions at aromatic compounds. 2 They proceed in most cases according to a S N 1 mechanism via a carbenium ion as key intermediate. 2,3 We have recently shown that the reaction of an a-chiral FriedelCrafts electrophile with various arenes can occur with high facial diastereoselectivity. 4 In these studies, the putative electrophile, i.e. cation 1, contained a stereogenic center, which carried a hydrogen atom and two alkyl groups. The alkyl groups differed significantly in size (methyl, tert-butyl) and this difference is likely to account for the diastereoface differentiation. We have now studied Friedel-Crafts reactions, in which precursors to the benzylic cations 2-4 ( Figure 1) served as substrates. 5 It was found that the polar chiral a-substituent induced a good to excellent facial diastereoselectivity. Figure 1 Chiral benzylic carbocations 1-4 formed as putative electrophilic intermediates in Friedel-Crafts alkylation reactions.The alcohols 5 and 6 (Scheme 1) were prepared by aldoltype reactions from para-methoxybenzaldehyde 6,7 while oxirane 7 was obtained from anethole by epoxidation. 8 Treatment of the electrophile precursors 5-7 with HBF 4 ·OEt 2 9 or BF 3 ·OEt 2 10 at low temperature in the presence of an arene (8) yielded the corresponding 1,1-diarylpropanes 9. The epimeric composition of the substrate did not influence the stereoselectivity, i.e. the reaction was stereoconvergent. 11 The results of the experiments are summarized in Table 1. All reactions gave predominantly a major diastereoisomer with product 9ba (entry 4) being the least selective example. In general, the reactions, in which 2-methylthiophene (8a) was used (entries 1, 4 and 8), were less diastereoselective than the reactions with the sterically more demanding nucleophiles 8b and 8c. For the epoxide opening, BF 3 ·OEt 2 showed an improved chemoselectivity as compared to HBF 4 ·OEt 2 as acidic catalyst (entries 7 and 8). The diastereoselectivity of the latter reaction, however, was slightly higher (vide infra).Scheme 1 Diastereoselective Friedel-Crafts alkylation reactions employing the chiral electrophiles 5-7 and arenes 8 as nucleophiles.The major diastereoisomers were in all three instances, i.e. for compounds 5, 6, or 7, the corresponding threocompounds threo-9a, threo-9b, or threo-9c. The configuration was proven for one representative example out of each series to establish the direction of face differentiation in a given carbenium ion 2, 3, or 4. The configuration assignment was most easily conducted for compound 9ac, which tu...

show abstract

“…Various alkynyl substituents containing a functional group can also be employed in this reaction as shown in Table 1. 7 In case of transformation of alkynylcyclopropanols with a substituent on the 2-position of the cyclopropane ring, two regioisomers, that is, the 4-substituted and/or 5-substituted 2-cyclopentenones can be formed, depending on which bond of the cyclopropane is cleaved (Scheme 5). Firstly the reaction of (1R*, 2S*)-2-methyl-1-phenylethynylcyclopropanol 6a cis (R=Ph, R 1 =Me, R 2 =R 3 =H) was examined according to the aforementioned procedure.…”

Section: Methodsmentioning

confidence: 99%

Cobalt Carbonyl Induced Transformations of Alkynyl- and Propadienyl-cyclopropanes

Iwasawa¹

1999

Synlett

Self Cite

View full text Add to dashboard Cite

A novel rearrangement of 1-(1-alkynyl)cyclopropanols to 2-cyclopenten-1-ones proceeded on complexation of their alkynyl part with Co 2 (CO) 8 . In the case of reactions of 1-alkynylcyclopropanols with an alkyl substituent on the cyclopropane ring, either 4-substituted or 5-substituted 2-cyclopenten-1-ones could be selectively obtained by appropriate choice of stereochemistry and protective group of the substrates. This rearrangement was successfully applied to the annulation of cyclopentenones onto cycloalkenes. Furthermore, the rearrangement was found to proceed catalytically on addition of triarylphosphite as a ligand. In particular, when tri(oisopropylphenyl)phosphite was used as ligand, 5-10 mol% of Co 2 (CO) 8 and 10-20 mol% of the phosphite sufficed for the efficient conversion of 1-alkynylcyclopropanols to 2-cyclopentenones. The same type of rearrangement proceeded when 1-[o-(1-alkynyl)phenyl]cyclopropanols were employed as substrate; these being converted to 2,3-dihydro-1-naphthalenone derivatives on heating their hexacarbonyldicobalt complexes in 2-propanol. Furthermore, a new type of isomerization-cyclization reaction proceeded to give 3a,4-dihydro-3H-cyclopenta[a]inden-2-one derivatives when the same reaction was carried out in the presence of DABCO. Finally a novel transformation of 1-(1,2-propadienyl)cyclopropanols into substituted 1,4-hydroquinones was developed utilizing the interaction of 1,2-propadienes and Co 2 (CO) 8 . This reaction was applied to the synthesis of vitamin E and K analogs.

show abstract

Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones via Their Hexacarbonyldicobalt Complexes. A New Use of Alkyne−Co₂(CO)₆ Complexes in Organic Synthesis

Cited by 74 publications

References 49 publications

Modern Developments in the Chemistry of Homoenolates

Modern Developments in the Chemistry of Homoenolates

Diastereoselective Friedel-Crafts Alkylation Reactions Employing Chiral Cation Precursors with Polar α-Substituents

Cobalt Carbonyl Induced Transformations of Alkynyl- and Propadienyl-cyclopropanes

Contact Info

Product

Resources

About

Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones via Their Hexacarbonyldicobalt Complexes. A New Use of Alkyne−Co2(CO)6 Complexes in Organic Synthesis

Cited by 74 publications

References 49 publications

Modern Developments in the Chemistry of Homoenolates

Modern Developments in the Chemistry of Homoenolates

Diastereoselective Friedel-Crafts Alkylation Reactions Employing Chiral Cation Precursors with Polar α-Substituents

Cobalt Carbonyl Induced Transformations of Alkynyl- and Propadienyl-cyclopropanes

Contact Info

Product

Resources

About

Rearrangement of 1-(1-Alkynyl)cyclopropanols to 2-Cyclopentenones via Their Hexacarbonyldicobalt Complexes. A New Use of Alkyne−Co₂(CO)₆ Complexes in Organic Synthesis