1,3‐Butadien‐2‐carbonsäuren aus dem Wittig‐Salz der 2‐(Brommethyl) acrylsäure

Düttmann, Hermann; Weyerstahl, Peter

doi:10.1002/cber.19791121015

Cited by 20 publications

(7 citation statements)

References 15 publications

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“…Clearly the 2-carbomethoxy group activates 11 toward dimerization since the known 0 -1 -methylthio-l,3-butadiene does not undergo Diels-Alder reactions (8). However, the sulfur also plays an activating role since the carbon analog of 11, ( a -1-ethyl-2-carbomethoxy-1,3-butadiene, does not dimerize readily (9).…”

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confidence: 99%

2-Carbomethoxy-1,3-butadiene: an electronically activated diene in [4 + 2] cycloadditions with electron-deficient dienophiles

Spino¹,

Crawford²

1993

Can. J. Chem.

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Cross Diels-Alder reactions between 2-carbomethoxy-l,3-butadiene 1 and electron-rich dienes were carried out. It was found that diene 1 had a higher reactivity than even the well-known Danishefsky diene in its Diels-Alder cycloaddition with electron-deficient dienophiles. In addition, (Z)-1-methylthio-3-carbomethoxy-l,3-butadiene 11 was found to have a higher reactivity than (Z)-I-methylthio-l,3-butadiene and (3-2-carbomethoxy-1,3-hexadiene, while both (a-and The facile dimerization of 2-carbomethoxy-l,3-butadiene 1 to give dimethyl mikanecate 4 has been known for some time (Scheme 1) (1, 2). Although the unusual ease with which this [4+2] cycloaddition takes place has been noted, a rationalization of this phenomenon has yet to be offered. A recent communication by Jung and Zimmerman provided the first kinetic data on this dimerization (3). They proposed that the high dienophilic character of the C1-C2 bond in 1 and the possibility that 1 may be more stable in its E-(s-cis) conformation could be major factors in accelerating this Diels-Alder reaction. W e provide evidence herein that another electronic factor plays a significant role in the rate acceleration of this dimerization and that in fact 1 should be regarded as an electronically activated diene.A 96% yield of dimer 4 was obtained by heating sulfolene 2 at 1 10°C (Scheme 1, method A) ( l a ) or by treating allylic bromide 3 with base at 25°C (Method B) ( I b). However, in the presence of the electron-rich diene 5 a (Y = Me) (4) and the very reactive diene 5 b (Y = OMe) (4b), either method led to a mixture of dimer 4 and cross cycloadduct 6 (Table 1). In most cases, the dimerization product prevailed unless a large excess of the electron-rich diene was used. Note that the lower temperature seems to favor dimerization over cross-cycloaddition (entries 3 , 4 , 5, and 8). These results indicate that diene 1 , as a dienophile, cycloadds more rapidly to itself, an electron-deficient diene, than it does to the electron-rich dienes 5 a and 5b. Note that the reactivity of diene 1 is underestimated here since diene 1 is generated slowly (3-4 h) and must be at low concentration relative to the other diene. W e ruled out the possibility of a local concentration effect, where molecules of diene 1 would dimerize faster because they were generated in proximity to one another, by stirring 1 equivalent each of sulfolene 2 and diene 5 b with '~u t h o r to whom correspondence may be addressed. excess methyl acrylate (10 equiv.) in refluxing toluene (Scheme 2). After 4 h, diene 1 had reacted completely to give 7 and Danishefsky's diene 5 b had reacted to the extent of 93% to give adduct 8 (gc analysis). Also detected were 6 b (<5%) and 4 (traces). Control experiments in which each diene was reacted separately with excess methyl acrylate confirmed that diene 1 reacted more rapidly with methyl acrylate than did Danishefsky's diene 56. We believe that diene 1 reacted as soon as it was generated since it (or dimer 4) was not detected in significant amount throughout the reactio...

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confidence: 99%

2-Carbomethoxy-1,3-butadiene: an electronically activated diene in [4 + 2] cycloadditions with electron-deficient dienophiles

Spino¹,

Crawford²

1993

Can. J. Chem.

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“…18 However, the sulfur also plays an activating role since the carbon analogue of 11, (Z)-2-methoxycarbonylhexa-1,3-diene 13, does not dimerise (Scheme 3). 11 En route to diene 15, the dianion of sulfolene 2 was acylated with methyl chloroformate to give a 78% yield of 14 (Scheme 4). 19 Upon heating in toluene for 12 h, 14 underwent a cheletropic elimination of SO 2 to afford the stable, but volatile, diene 15 as a 1 : 1 mixture of E-and Z-isomers.…”

Section: Resultsmentioning

confidence: 99%

“…Yields of dimerisation are high regardless of diene concentration (including in the neat form) with no trace of [2 ϩ 2]-or [4 ϩ 4]cycloaddition or polymerisation products. More convincingly, (Z)-2-methoxycarbonylhexa-1,3-diene 13 (see Scheme 3) does not dimerise and is quite stable 11. This compound would behave just like diene 1 if a diradical mechanism were operational but it is not expected to dimerise easily via a concerted cycloaddition because of the Z-geometry of the double bond.…”

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confidence: 98%

The dimerisation of 2-methoxycarbonylbuta-1,3-diene: the importance of paralocalisation energy in assessing diene reactivity

Spino¹,

Crawford²,

Cui³

et al. 1998

J. Chem. Soc., Perkin Trans. 2

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The dimerisation and competitive cycloaddition of 2-methoxycarbonylbuta-1,3-diene with electron-rich dienes has been investigated. Experimental results provide evidence that the enthalpy of the -system significantly influences the energy of the transition state of cycloadditions of this type. This has been corroborated by ab initio calculations. We propose an early reorganisation of the -electrons in such cycloadditions to explain the influence stated above.

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“…, 5.12. l-(2,2-Dimethyl-l-oxopropoxy)-8-ethyl-6if-benzo[cf ]naphtho[ 1, [2][3][4][5][6] ]pyran-6-one (10c). A solution of pivaloate ester 6c (0.376 g, 0.99 mmol) in carbon tetrachloride with NBS (0.336 g, 1.9 mmol) and benozyl peroxide (35 mg) was heated to reflux for 30 min.…”

Section: Methodsmentioning

confidence: 99%

The photobiology of the gilvocarcins. Total synthesis of defucogilvocarcin V and a related photoactive vinyl phenol

McGee¹,

Confalone²

1988

J. Org. Chem.

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1,3‐Butadien‐2‐carbonsäuren aus dem Wittig‐Salz der 2‐(Brommethyl) acrylsäure

Cited by 20 publications

References 15 publications

2-Carbomethoxy-1,3-butadiene: an electronically activated diene in [4 + 2] cycloadditions with electron-deficient dienophiles

2-Carbomethoxy-1,3-butadiene: an electronically activated diene in [4 + 2] cycloadditions with electron-deficient dienophiles

The dimerisation of 2-methoxycarbonylbuta-1,3-diene: the importance of paralocalisation energy in assessing diene reactivity

The photobiology of the gilvocarcins. Total synthesis of defucogilvocarcin V and a related photoactive vinyl phenol

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