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Transannular aldol reaction

In a recent total synthesis of the novel neurotrophic agent merrilactone A (22, Scheme 4) by Inoue and Hirama [24], key intermediate 21 with the cis-bicyclo[3.3.0] octane framework embedded within the caged pentacycle 22 was elaborated from cyclobutane 18 by a sequence of RCM and immediate cleavage of the resulting bicyclic vicinal diol 19 to raeso-diketone 20. Cyclooctenedione 20 then underwent regioselective transannular aldol reaction at low temperature (LHMDS, THF, -100 °C) to produce a 3 1 mixture of isomers in 85% combined yield. The major isomer 21 with the required stereochemistry was then converted into the racemic natural compound ( )-22 in 19 steps. [Pg.278]

Scheme 4 A sequence of RCM-glycol cleavage-transannular aldol reaction in Inoue s total synthesis of merrilactone A (22) [24]... Scheme 4 A sequence of RCM-glycol cleavage-transannular aldol reaction in Inoue s total synthesis of merrilactone A (22) [24]...
Proline is effective in mediating an asymmetric transannular aldol reaction." ... [Pg.371]

The intramolecular aldol reaction is an often used approach to the synthesis of cycUc compounds, especially five- and six-membered rings [23]. The two carbonyl components of the substrate react intramolecularly as both electrophiles and as nucleophiles in addition, they form two different nucleophilic intermediates, namely, endo 40 and exo 41 aldol (Figure 28.4). Another type of intramolecular reaction is the transannular aldol reaction, which may be considered as simultaneously endo and exo. [Pg.799]

Hirsutene (50) Scheme 28.4 Intramolecular transannular aldol reactions. [Pg.801]

The aldol reaction plays a key role in biosynthesis of poly-ketide natural products. It is also one of the most used transformations for stereoselective C—C bond formation. Deslongchamps and co-workers described one of the early examples of transannular aldol reactions in the synthesis of (it)-ryanodol, a compact and highly functionalized polycyclic diterpenoid isolated from Ryania speciosa The 1,5-diketone 48 that was requisite for the transannular aldol reaction was generated in situ from 47 by ozonolysis of its alkene (Scheme 20.14). Conformational equilibration of 48 to the less strained conformer B was followed by a transannular aldol reaction to give 49 in 90% yield. The polycyclic molecular framework provided the conformational bias for stereoselective formation of 49, which was converted to ryanodol after additional transformations. [Pg.558]

SCHEME 20.14. The transannular aldol reaction in the synthesis of ( )-ryanodol. [Pg.559]

Miyakolide, a bryostatin-like macrolide isolated from the sponge Polyflbrospongia sp., was synthesized by Evans and co-workers using a transannular aldol reaction for formation of part of the polycyclic ring system. ... [Pg.559]

Whereas the enaminone 50 would not undergo the transannular aldol reaction (Scheme 20.15), treatment with 1.5 equiv of TsOH in MeCN-water (5 1) for 18 hours followed by addition of a pH 10 buffer led to clean formation of 52. [Pg.559]

This one-pot sequence involved hydrolysis of the enami-none to give 1,3-diketone 51, hydrolysis of its methyl lactal, a transannular aldol, and an intramolecular hemiketaliza-tion. Although four diastereomeric products were theoretically possible, the transannular aldol reaction proceeded stereoselectively to give the desired 52 as the final product. This reflected the inherent conformational bias of the mac-rocyclic precursor. [Pg.560]

A transannular aldol reaction is also part of the squa-rate ester cascade applied by Paquette and co-workers in their expeditious 10-step synthesis of hypnophilin, an antibiotic metabolite isolated from cultures of the fungus Pleurotellus hypnophilus. Sequential 1,2-additions of a pair of vinyl lithium reagents to the squarate ester 54 led to intermediates (i.e., 56 and 58) by either trans- or... [Pg.560]

Whereas the examples above used substrate control for stereoselective transannular aldol or related reactions, reagent control has also been reported for the transannular aldol reactions. One example is synthesis of the musk ordorants (R)-muscone and (R,Z)-5-muscenone by Knopff and co-workers. It involved enantioselective formation of 73 by the transannular aldol condensation of the symmetrical macrocyclic 1,5-diketone 72 using sodium ephedrate for desymmetrization (Scheme 20.19). The reaction was assumed to proceed by a reversible transannular aldol reaction followed by an enantioselective dehydration reaction. [Pg.561]

Since intramolecular transannular aldol reactions create two new rings and at least two new stereogenic centers in a single process, the corresponding cyclic p-hydroxy ketones are useful for the synthesis of polycyclic natural products. The trons-4-fluoro proline 48 is superior to (S)-proline in catalysis of this type of reaction, affording excellent diastereoselectivity and enantioselectivity (Scheme 28.4). The utility of this reaction has been demonstrated in a total synthesis of (-l-)-hirustene (50), is a fungal metabolite first isolated from the basidiomycete Coriolus consors [27]. [Pg.800]


See other pages where Transannular aldol reaction is mentioned: [Pg.155]    [Pg.494]    [Pg.206]    [Pg.155]    [Pg.255]    [Pg.4]    [Pg.292]    [Pg.4]    [Pg.1072]    [Pg.1435]    [Pg.560]    [Pg.562]    [Pg.563]    [Pg.563]    [Pg.563]    [Pg.575]    [Pg.1072]   
See also in sourсe #XX -- [ Pg.4 ]

See also in sourсe #XX -- [ Pg.4 ]

See also in sourсe #XX -- [ Pg.4 ]

See also in sourсe #XX -- [ Pg.800 , Pg.801 , Pg.1072 ]




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Transannular reactions

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