Tetracyclic bridged

Kauran Type, Phyllocladane Type, Tetracyclic (Bridged)... 

The reaction of relatively simple starting materials, coumarin 40, piperidone 37 and ammonium acetate, leads in a single step to the complex bridged tetracyclic compound 44. The reaction can be rationalized by assuming formation of the iminc 38 from reaction of 37, with ammonia. Conjugate addition of the eneamine-like tautomer 39 to the excellent Michael acceptor 40 will... 

In the event, macrocyclic bis(thiolactones) perform admirably in the macrocycle-to-bicycle bridging reaction (see Scheme 5).17 For example, the eis-fused tetracycle 25 can be produced, in 80%... 

Similarly, efficient tetracyclization (MeAlCl2-promoted) of the bis-allylic silane/ bis-epoxide 97 constitutes the key step in the synthesis of (+)-a-onocerin. In this case, because of the presence of the bis-allylic silane group, a double bis-annula-tion occurs, with the formation of the ethylene-bridge linked bis-decalin system present in the target compound (Scheme 8.26) [46],... 

Knolker and coworkers also used a domino [3+2] cycloaddition for the clever formation of a bridged tetracyclic compound 4-172, starting from a cyclopentanone 4-168 and containing two exocydic double bonds in the a-positions (Scheme 4.36) [57]. The reaction of 4-168 with an excess of allylsilane 4-169 in the presence of the Lewis acid TiCLj led to the spiro compound 4-170 in a syn fashion. It follows a Wag-ner-Meerwein rearrangement to give a tertiary carbocation 4-171, which acts as an electrophile in an electrophilic aromatic substitution process. The final step is the... 

Intramolecular Sn2 reactions of lactams 376 and 377 (see Scheme 85, lower part) produced nitrogen- and oxygen-bridged, highly strained products 378, 379, and 380, forming densely functionalized tetracyclic frameworks of the tetrahydroisoquinoline alkaloids (08TL5141). 

However, 2-bromotetradeca-l,13-dien-7-ynes such as 96 n = 1), which were set up to furnish decahydrophenan-threne skeletons (6-6-6-tricycles), gave the interesting tetracyclic compounds 97 (n=l) with a cyclopropane moiety bridging the A- and B-ring junction (Scheme 27). " " ... 

Thermal bond transposition has been utilized successfully in the synthesis of a number of relatively heat-insensitive families of heteroannulenes, such as the triheteronin frame (20) constructed thermally from the tetracyclic valence tautomer and the tetrabenzo heteronins (18) obtained by thermal bond transposition of their spirostructured valence tautomers (113). Similarly, thermally induced bridge extrusion (C02) has been utilized as a means of preparing dihydrobenzazonine (112) (the direct photoprogenitor of aza[13]annulene 36a) from cycloadducts (104) (73TL3805). 

In an approach to the clavine alkaloids [170] based on intramolecular nitrone-alkene cycloaddition, the condensed tetracyclic system is probably favored by steric factors. Equilibration at higher temperature leads to predominantly a bridged oxabicyclo-[3.2.1]nonae derivative in which a portion of the molecule contains polarity alternation sequence (OCOC=0, N-C-C-C=0). 

Reaction of triazolopyrimidinium ylides (256) with active acetylenes gave the 1 2 adducts 260. The formation of 260 may occur in two ways the shortest pathway consists of the double 1,3-dipolar cycloaddition of the diylide 256A with two molecules of the acetylene at two different sites to form the tetracyclic adduct 257, followed by ring opening under basic conditions to give 260. The second pathway consists of cycloaddition between the ylide carbanion of 256 and the bridged carbon C-4 to form the 1 1 adduct 258, which isomerizes to the more stable compound 259, which may be formed directly by the cycloaddition at the ylide carbanion and C-2. The second cycloaddition afforded the 1 2 adduct 257 [87JCS(P1)2531] (Scheme 49). 

The first synthesis of the tetracyclic integrastatin nucleus involves a benzylic oxidation of a bridged isochroman using PDC in the presence of /-butylhydroperoxide (TBHP) <20030L4441, 20050BC756>. 

Similarly, Chung et al. described a cobalt-catalyzed route to 5.5.5.6 tetracyclic compounds. Tetracyclic dienones were prepared by double Pauson-Khand reaction of triynes. Interestingly, reactions of triynes such as 38 with CO in the presence of 2.5 mol% of Co2(CO)s did not give any [5.5.5.5]fenes-trane derivative but a bridged system (39) (Scheme 19). 

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