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Sigmatropic rearrangements Claisen rearrangements Cope

Tandem [3,3]—[3,3] Sigmatropic Rearrangements Claisen-Cope Rearrangements... [Pg.411]

Citral is a key intermediate in the synthesis of vitamin A, and in Chapter 31 you had a go at designing a synthesis of it. BASF manufacture citral by a remarkable process that involves two successive [3,3] -sigmatropic rearrangements, Claisen followed by a Cope. [Pg.949]

Carbamimidoyl isothiocyanates on heating easily undergo irreversible isomerization to afford quinazoline-4(3//)-thiones. The reaction comprises two sigmatropic rearrangements (a Claisen rearrangement and a Cope rearrangement) both are allowed according to the Woodward-Hoffmann rules. [Pg.56]

Two other examples of carbanion -accelerated rearrangements have been described in the literature. The first one leads from the anion of the 60-allylic guanine 211 in two consecutive [3.3] sigmatropic shifts (a combined Claisen-Cope rearrangement) via 212 and 213 to the 8-allylic guanine 214 173). [Pg.48]

In this case, the ability to use a sulfide in place of a sulfoxide, with the oxidation-state adjustment and subsequent Mislow-Evans to occur later, provided a solution to the recalcitrant Claisen rearrangement. This strategy f Scheme 18.51) was particularly appealing in this case, because terminal thioethers are known to be strongly activating for [3,3]-sigmatropic anionic oxy-Cope rearrangements. ... [Pg.726]

This rearrangement also involves [3, 3]-sigmatropic pathway like cope-rearrangement. However, in Claisen rearrangement the substrate incorporates one or more heteroatoms in place of carbon in 1, 5-hexadiene system. Simplest example of Claisen-rearrangement is thermal conversion of allyl-vinylether to 4-pentenal ... [Pg.91]

Two other important sigmatropic reactions are the Claisen rearrangement of an allyl aryl ether discussed in Section 18.4 and the Cope rearrangement of a 1,5-hexadiene. These two, along with the Diels-Alder reaction, are the most useful pericyclic reactions for organic synthesis many thousands of examples of all three are known. Note that the Claisen rearrangement occurs with both allylic aryl ethers and allylic vinylic ethers. [Pg.1193]

C4-insertions by means of a sigmatropic rearrangement process have been described using either a thermal Cope reaction, anionic Claisen amide enolate and zwitterionic aza-Claisen rearrangements. [Pg.173]

The second largest group of pericyclic domino reactions starts with a sigmatropic rearrangement, which is most often a Claisen or an oxa- and aza-Cope rearrangement however, some processes also exist with a 2,3-sigmatropic rearrangement as the second step. [Pg.280]

Domino reactions starting with a sigmatropic rearrangement have long been known. Most of these processes use a Cope or Claisen rearrangement [77], followed by another Cope or Claisen rearrangement. [Pg.313]

Therefore, the [3, 3] sigmatropic rearrangement has become a useful tool in synthetic organic chemistry. The following are some examples which include Cope and Claisen rearrangement. [Pg.84]

So we find that both Cope and Claisen rearrangements are [3, 3] sigmatropic rearrangements and proceed by suprafacial-suprafacial pathway. [Pg.91]

This section will focus on recent examples of asymmetric [3,3]-sigmatropic rearrangements involving dienes and polyenes. Attention will be given to Cope and Claisen rearrangements, as well as to several of their variants. For more exhaustive reviews of the subject, the reader is referred elsewhere69,70. [Pg.722]

A sigmatropic rearrangement "is said to be of order [ j] when a o bond, flanked by one or more n electron systems, migrates to a new position whose termini are i-1 and j-1 removed from the original bonded loci, in an uncatalysed intramolecular process" [23]. Thus the well known Claisen and Cope rearrangements, for example, are sigmatropic rearrangements of the order [3,3]. [Pg.136]

The Cope, oxy-Cope, and anionic oxy-Cope rearrangements belong to the category of [3,3J-sigmatropic rearrangements. Since it is a concerted process, the arrow pushing here is only illustrative. Cf. Claisen rearrangement. [Pg.151]


See other pages where Sigmatropic rearrangements Claisen rearrangements Cope is mentioned: [Pg.789]    [Pg.789]    [Pg.411]    [Pg.411]    [Pg.796]    [Pg.796]    [Pg.241]    [Pg.241]    [Pg.445]    [Pg.1198]    [Pg.17]    [Pg.213]    [Pg.1450]    [Pg.171]    [Pg.561]    [Pg.1335]    [Pg.374]    [Pg.276]    [Pg.83]    [Pg.722]    [Pg.861]    [Pg.149]    [Pg.150]    [Pg.165]    [Pg.348]    [Pg.383]    [Pg.282]    [Pg.175]   


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Claisen-Cope rearrangement

Sigmatropic -rearrangements Claisen rearrangement

Sigmatropic -rearrangements rearrangement

Sigmatropic Claisen

Sigmatropic Shifts Cope and Claisen Rearrangement

Sigmatropic rearrangements Cope rearrangement

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