Carpanone, synthesis

Carcerands 1427-1429—see also Hemicarcerands Carceroisomerism 1430 Carpanone, synthesis of 1311... 

Use of the immobilized iridium double-bond isomerizing catalyst (70) developed for the carpanone synthesis again worked well to convert commercially available 73 to the conjugated product (74). This was then methylated in the presence of PS-BEMP (7), a reaction that proceeds in almost quantitative yield. Next, an asymmetric dihydroxylation was performed according to methods developed by Sharpless. However, instead of using a conventional workup procedure for the vicinal diol (75), a new catch-and-release protocol was developed. This made use of the immobilized boronic acid (76) to trap the chiral diol... 

The elegant biomimetic synthesis of carpanone by Chapman and coworkers commences with the base-induced isomerization of 2-allyl-4,5-methylenedioxyphenol (4)3 to 2-(/ran.y-l-propenyl)-4,5-methylenedioxyphenol (3) (see Scheme 2). Compound 3, as simple as it is, is actually the key intermediate in this synthesis oxidative dimerization of 3 could result in the formation of carpanone (1) through the intermediacy of the C2-symmetric and highly reactive bis(quinodimethide) 2. 

Organic syntheses based on biosynthetic proposals are often extremely concise and elegant.6 Although the constitution and stereochemical complexity of carpanone may seem formidable, the sequential application of the Diels-Alder and oxidative phenolic coupling transforms7 to the natural product provides an exceedingly efficient solution. Chapman s striking synthesis of carpanone typi-... 

In their synthesis of the natural product carpanone, Ley and coworkers described the microwave-assisted Claisen rearrangement of an allyl ether (Scheme 6.80 a)... 

Baxendale IR, Lee A-L, Ley SV (2001) A concise synthesis of the natural product carpanone using solid-supported reagents and scavengers. Synlett 482-484... 

Another example is the synthesis of carpanone (23), which takes place by a two-step dimerisation of two identical moieties (22). the second step proceeding via a hetero-Diels-Alder cycloaddition [19] (Scheme 4.5). 

As already shown in Scheme 8, carpanone (44) has been synthesized by an electrochemical method. More efficient synthesis of 44 was effected with O2 catalyzed by metal-Schiff base complexes. Of the four complexes, Co(II)(salpr), Co(ll)(salen), Fe(II)(salen) and Mn(ll)(salen), Co(ll)(salen) provides the best results its solution with 4,5-methylenedioxy-... 

SCHEME 54. Synthesis of carpanone using 02-Co(II)(salen) complex... 

Scheme 8.42 Total synthesis of Carpanon utilizing resin-bound reagents and polymers.

In 2002, Ley reported the application of resin-bound reagents and polymers towards the synthesis of carpanone [57]. In the final steps towards carpanone, a resin-bound Co(salen) catalyst was used to give the desired intermediate along with the formation of a small amount of aldehyde by-product. To remove this byproduct, a resin-bound tris-amine scavenger was used, yielding the desired product in high purity (Scheme 8.42). 

Since the remarkable demonstration of the facility of an intramolecular Diels-Alder reaction (dimerization) of an o-quinone methide, generated by the oxidation of a substituted o-alkylphenol in the development of a biomimetic synthesis of carpanone [Eq. (44)],170... 

Polymer-supported reagents have been applied to the synthesis of the natural product carpanone, resulting in a clean and efficient synthesis without the need for a conventional... 

Polymer-supported phosphazene bases (of which one example is commercially available) can be used to deprotonate a phenol group for allylation in the generation of an intermediate during an efficient synthesis of the natural product carpanone [48]. Such a system was also employed for a dehydration step in the synthesis of 1,3,4-oxadiazoles [49]. 

Phenols and phenolic residues are also present in many other natural products. Consequently, the procedures used for the synthesis of carpanone above could readily be adapted, for example, in the preparation of polysphorin and related neolignins. Interest in these... 

Scheme 18.24 Synthesis of polysphorin utilizing the polymer-supported iridium catalyst used in i key step in the synthesis of carpanone.

A number of heterocyclics such as coumarins, flavones, and quino-lones have been prepared from o-subst. co-(methylsulfinyl)aceto-phenones . A simple isoindole synthesis with hydrazines has been published Phenolic coupling with PdCl2 has been used efficiently to produce carpanone whereby five contiguous asym. centers with the correct stereochemistry have been introduced in a single step . A facile synthesis of the tetracyclic skeleton of rheadan alkaloids, whidi have a characteristic azepine ring, has been reported Benzimidazoles and benzoxazoles have been prepared by a novel ring closure of a-amino-/9,7-ethylenenitriles . ... 

FIGURE 11.91 Solid-phase biomimetic synthesis of carpanone-like molecules. (From Lindslay, C.W. et al., Solid-phase biomimetic synthesis of carpanone-like molecules, J. Am. Chem. Soc., 122, 422, 2000.)... 

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