Diels transannular, biomimetic

An enantioselective biomimetic synthesis of longithorone A was accomplished on the basis of proposed biosynthesis. " The syntheses of two [12]-paracyclophanes 105 and 107 are realized by applying ene-yne metatheses macrocyclization to 104 and 106, which are synthesized from the common substrate 103. Longtholone A is constructed using intermolecular and transannular Diels-Alder reactions followed by oxidation (Scheme 40). 

Studies toward the biomimetic total synthesis of (+)-chatancin were conducted by P. Deslongchamps et al. The authors planned to use a transannular Diels-Alder reaction of a pyranophane intermediate as the key ring forming step. The cyclic dienedione precursor for this transformation was prepared using the Prins reaction on a substrate derived from trans-trans farnesol. 

Li and Pattenden have proposed a biomimetic approach to the diterpenoid plumarellides, by a transannular Diels-Alder (TADA) reaction on cembra-noids prepared in their laboratory. The macrocyclic compounds are prepared by an RCM as a key step, and the TADA produces the polycyclic core with a seven-membered ring as a result of the spacer (Scheme 63) [101]. 

Transannular Diels-Alder reaction is also one of the most prominent synthetic methods of intramolecular Diels-Alder reaction. The applications of transannular Diels-Alder reaction are mostly found in biomimetic synthesis. The reasonable use of transannular Diels-Alder strategy can significantly simplify the synthesis route and improve the artistic quality of synthesis, and at the same time, it can also provide a meaningful reference for the speculation of the routes of biosynthetic... 

In 2003, Deslongchamps and coworkers reported an elegant synthesis of (+)-chatancin (112) in 17 steps involving a biomimetic transannular cycloaddition (Scheme 8.18) [48]. Although there are no evidences of in vivo transannular Diels-Alder (TADA) reaction in cembranoids, Deslongchamps hypothesized that 112 could be obtained from a macrocyclic pyranophane such as 116a. To verify... 

Debenzoyltashironin, a densely functionalized polycyclic natural product that induces neurite outgrowth in fetal rat cortical neurons, was synthesized by Danishefsky and co-workers using a biomimetic synthetic route. As shown in Scheme 20.4, the cyclic quinone monoketal 10 was formed by oxidative dearomatization of 9 followed by intramolecular O-cyclization. The transannular Diels-Alder cycloaddition was observed during this process. However, a 4-minute microwave irradiation was needed to complete the reaction to give 11 in 65% yield. It is remarkable that such a complex polycyclic ring system was assembled in two steps. Incorporation of a trisubstituted allene as the dieno-phile of 9 was important because the transannular Diels-Alder reaction did not proceed when an alkene dienophile... 

An enantioselective biomimetic synthesis of (—)-longithorone A was accomplished on the basis of the proposed biosynthesis [llj. Two [12]-paracyclophanes 25 and 26 were synthesized from common intermediate 27 by applying ene-yne metathesis macrocyclization in 42 and 31% yields, respectively. Intermolecular Diels-Alder reaction of 25 and 26 provided 32. Deprotection followed by oxidation gave 33, which spontaneously gave longithorone A via transannular Diels-Alder reaction (Scheme 6.8). 

More recently, Lee et al. have also employed this strategy for the construction of the B/Z-1,3-butadiene motif required for the synthesis of (—)-cochleamycin A using a biomimetic type transannular Diels-Alder reaction, (Figure 8.10) [38]. The enantiomer exhibits antimicrobial activity against Gram-positive bacteria and has modest cytotoxic activity. The unsymmetrical bis-alkoxyalkynylsilane 85 was prepared as a mixture of diastereoisomers at silicon by the addition of the secondary alcohol 84 to the bis-alkynylsiloxane 83 (Scheme 8.16). Although the... 

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See also in sourсe #XX -- [ ]

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