Stereocontrolled Synthesis of Acyclic Tri- and Tetra-C-Substituted α-Alkoxymethyl α,β-Unsaturated Esters

Hall, Dennis G.; Chapdelaine, Daniel; Préville, Patrice; Deslongchamps, Pierre

doi:10.1055/s-1994-22966

Cited by 24 publications

(13 citation statements)

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“…9 The conjugate addition of organocopper reagents to acetylenic esters is a prime method to access isomerically pure, trisubstituted R,β-unsaturated esters. 10 Unfortunately, extensions toward synthesizing tetrasubstituted alkenes 11 have been hampered by the low reactivity of 1-alkoxycarbonyl vinylcopper(I) intermediate 3 and its tendency to isomerize via a copper allenoate (4) at temperatures above -30 °C (Figure 1). 12 Yet we anticipated that halomethylboronates (6-8) could be sufficiently reactive, under optimal conditions, to trap 3 with no loss of stereochemical integrity and afford tetrasubstituted allylboronates 9 with overall cis-addition.…”

mentioning

confidence: 99%

Novel Isomerically Pure Tetrasubstituted Allylboronates: Stereocontrolled Synthesis of α-Exomethylene γ-Lactones as Aldol-Like Adducts with a Stereogenic Quaternary Carbon Center

Kennedy

Hall

2002

J. Am. Chem. Soc.

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In spite of their inherent isomerization tendency and low reactivity, 1-alkoxycarbonyl vinylcopper(I) intermediates from the conjugate addition of organocuprates onto acetylenic esters were trapped with very high cis-addition selectivity with iodomethylboronic esters in the presence of HMPA. The resulting isomerically pure 3,3-disubstituted allylboronates react with aldehydes in a highly diastereo- and enantioselective manner, providing alpha-exomethylene gamma-lactones with a stereogenic quaternary beta-carbon center.

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confidence: 99%

Novel Isomerically Pure Tetrasubstituted Allylboronates: Stereocontrolled Synthesis of α-Exomethylene γ-Lactones as Aldol-Like Adducts with a Stereogenic Quaternary Carbon Center

Kennedy

Hall

2002

J. Am. Chem. Soc.

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“…The only product seen after protonation, 5 , has the Z-configuration 8a, The assignment of chemical shifts in the spectra above (Figure ) was further supported by the NMR investigations of 1 with methyl 4,4-dimethyl-2-pentynoate ( 6 ) and its two 13 C-labeled analogues, labeled at C1 and C3, respectively . The decrease of 62 Hz in 1 J 2,3 upon π-complex formation ( 7 ) firmly establishes that the triple bond is coordinated to the cuprate.…”

mentioning

confidence: 71%

“…So far no organocopper coordination to acetylenic Michael acceptors has been detected in solution, mostly because these types of substrates are far too reactive toward organocuprates. Electrophilic trapping, IR measurements, and NMR spectroscopy of the intermediates after the C−C bond formation has taken place imply the existence of adducts with vinylcopper structures in some cases and copper allenolate structures in others (see Scheme ).…”

mentioning

confidence: 99%

NMR Spectroscopic Evidence for π-Complexation and the Formation of a Vinylcopper Intermediate in the Reaction between Methyl phenylpropiolate and ^tBuCu(CN)Li

1996

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“…The E -and Z -structure is determined from spectroscopic data 4,5,10,14 of the functional allylic alcohols 3 and 4 and by comparison with data of various authentic samples. 15 From Table 1, it is clear that the stereochemistry of the formylation reaction is dependent on the nature of electron-withdrawing group. With EWG = CN, the stereoselectivity of the new allylic alcohols 3a-g seems to depend both on steric and electronic effects and gives E -functional olefins for an electron-withdrawing group (R = p -CF 3 C 6 H 4 ).…”

Section: A New and Efficient Methods For The Isomerization Of Secondarmentioning

confidence: 99%

A New and Efficient Method for the Isomerization of Secondary Functional Allylic Alcohols into their Primary Isomers

Beltaïef¹,

Hbaïeb²,

Besbes³

et al. 1998

Synthesis

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The first efficient tandem: "bromination-formylationhydrolysis" for the 1,3-transposition of acyclic allylic alcohols 1 and 2 bearing a nitrile and an ester group is reported.While the Baylis-Hillman reaction produces highly functionalized alkenes 1 of types 1 and 2, which have been demonstrated to be versatile and useful intermediates in the synthesis of natural products 2 and biologically active compounds, 3 this methodology is not efficient for the production of the corresponding 3-substituted allylic alcohols 3 and 4 . The latter compounds are important raw materials for the food industry, 4 as well as intermediates for the synthesis of Nuciferol derivatives, 5 sesquiterpenes lactones, 6 and antifungal and antibacterial products. 7 To our knowledge, few preparations of 3 8 or 4 9 (Scheme 1) have been described.A recent publication 10 on the first synthesis of 3-substituted 2-cyanoallylic alcohols 3 based on reduction of 2-cyano-2,3-epoxy esters prompts us to describe our own results. As part of our ongoing work on the synthesis of novel 2-functional allylic alcohols 3 and 4 , we report here a general and convenient method to accomplish the rearrangement of Baylis-Hillman products 1 and 2 to the corresponding primary allylic alcohols 3 and 4 using a threestep reaction sequence (bromination-formylation-hydrolysis). 11 The sequence involves a regiospecific 1,3-allylic transposition of the hydroxy group (Scheme 2).Our methodology is based on the treatment of 2-(hydroxyalkyl)acrylic compounds 1 and 2 with PBr 3 in diethyl ether at 0°C leading respectively to allylic bromides 5 as a mixture of E , Z-isomers in which the E -isomer is strongly predominant (EWG = CN) and exclusively the Zisomer when EWG = CO 2 Et. The stereochemistry of allyl bromides was assigned by comparing 1 H and 13 C NMR spectral data of these molecules reported in literature. 12 Thus, the displacement of bromide using triethylammonium formate (TEAF; 2 Et 3 N-5 HCO 2 H) as formylating reagent 13 , has been carried out in refluxing acetonitrile. The formyloxy nitriles and esters 6 are hydrolyzed to the corresponding alcohols 3a-g and 4a-h upon hydrolysis in the presence of one drop of concentrated hydrochloric acid at room temperature. 2-(Hydroxymethyl)alk-2-enenitriles 3a-g and ethyl 2-(hydroxymethyl)alk-2-enoates 4a-h prepared are summarized in Table 1.The E -and Z -structure is determined from spectroscopic data 4, 5, 10, 14 of the functional allylic alcohols 3 and 4 and by comparison with data of various authentic samples. 15From Table 1, it is clear that the stereochemistry of the formylation reaction is dependent on the nature of electron-withdrawing group. With EWG = CN, the stereoselectivity of the new allylic alcohols 3a-g seems to depend both on steric and electronic effects and gives E -functional olefins for an electron-withdrawing group (R = p -CF 3 C 6 H 4 ). In contrast, the transformation of secondary alcohols 2 into the corresponding primary alcohols 4a-h is highly stereoselective, independent of the nature of the R group and lea...

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Stereocontrolled Synthesis of Acyclic Tri- and Tetra-C-Substituted α-Alkoxymethyl α,β-Unsaturated Esters

Cited by 24 publications

References 0 publications

Novel Isomerically Pure Tetrasubstituted Allylboronates: Stereocontrolled Synthesis of α-Exomethylene γ-Lactones as Aldol-Like Adducts with a Stereogenic Quaternary Carbon Center

Novel Isomerically Pure Tetrasubstituted Allylboronates: Stereocontrolled Synthesis of α-Exomethylene γ-Lactones as Aldol-Like Adducts with a Stereogenic Quaternary Carbon Center

NMR Spectroscopic Evidence for π-Complexation and the Formation of a Vinylcopper Intermediate in the Reaction between Methyl phenylpropiolate and ^tBuCu(CN)Li

A New and Efficient Method for the Isomerization of Secondary Functional Allylic Alcohols into their Primary Isomers

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Stereocontrolled Synthesis of Acyclic Tri- and Tetra-C-Substituted α-Alkoxymethyl α,β-Unsaturated Esters

Cited by 24 publications

References 0 publications

Novel Isomerically Pure Tetrasubstituted Allylboronates: Stereocontrolled Synthesis of α-Exomethylene γ-Lactones as Aldol-Like Adducts with a Stereogenic Quaternary Carbon Center

Novel Isomerically Pure Tetrasubstituted Allylboronates: Stereocontrolled Synthesis of α-Exomethylene γ-Lactones as Aldol-Like Adducts with a Stereogenic Quaternary Carbon Center

NMR Spectroscopic Evidence for π-Complexation and the Formation of a Vinylcopper Intermediate in the Reaction between Methyl phenylpropiolate and tBuCu(CN)Li

A New and Efficient Method for the Isomerization of Secondary Functional Allylic Alcohols into their Primary Isomers

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NMR Spectroscopic Evidence for π-Complexation and the Formation of a Vinylcopper Intermediate in the Reaction between Methyl phenylpropiolate and ^tBuCu(CN)Li