Cyathins

The Williams approach to bicyclo[5.4.0]undecane containing molecules such as the cyathins, striatins, dolastanes, clavularanes, grayanotoxins, tiglianes, and daphnanes also utilizes an oxidopyrylium cycloaddition to generate the ether constrained bicyclic (Scheme 4.81) (164). The object of the Williams study was to prepare the bicyclo[5.4.0]undecanes and investigate the regio- and stereocon-trolled oxidation of the substrate. 

Cycloadducts have also been used as starting materials for the synthesis of the C29-C37 segment of a spongistatin <99TA1539> and the synthesis of the cyathin core <990L1535>. 

In a study aimed at synthesizing the cyathin diterpene skeleton, another pyrylium ylide-alkene [5+2] cycloaddition was employed (as shown in Scheme 13) <1999T3553>. 

A hydroxylative Knoevenagel reaction of the aldehyde 873 proceeds in the presence of phenylsulfinyl acetonitrile to afford the 5,6-dihydropyran-2-one 874, an intermediate during the enantioselective total synthesis of (+)-allo-cyathin B2 (Scheme 242) <2005JA10259>. 

The intermolecular [2 + 2]-photocycloaddition of para-tetrahydronaphthoqui-nones has been applied by Ward et al. to the synthesis of cyathin diterpenes [52], An example is represented by the total synthesis of ( )-allocyathin B3 (46), during the course of which the diastereoselective [2 + 2]-photocycloaddition of allene to substrate 44 served as one of the pivotal steps (Scheme 6.17) [53]. The addition delivered a mixture of regioisomers (r.r. = 80/20), from which compound 45 was separated. The facial diastereoselectivity was perfect due to the concave shape of the quinone. 

Ward, D.E. and Shen, J. (2007) Enantioselective total synthesis of cyathin A3. Organic Letters, 9,... 

SCHEME 128. Construction of the tricyclic core of cyathins by a Brook mediated [3 + 4] annulation599... 

The anodic cyclization reaction of furans was applied as a key step to construct the [5-6-7]-fused tricyclic core of cyathins <19990L1535>, and the [5-6-5]-fused tricyclic core of alliacol A using the acyclic silyl enol ether tethered furan 34 during its total synthesis (Scheme 21) <2004JA9106, 2003JA36>. 

D.E. Ward et al. reported a general approach to cyathin diterpenes and the total synthesis of allocyathin 63. The tetracyclic secondary alcohol was converted to the corresponding ketone using TPAP/NMO in good yield. ... 

Takeda, K., Nakane, D., Takeda, M. Synthesis of the Tricyclic Skeleton of Cyathins Using Brook Rearrangement-Mediated [3 + 4] Annulation. Org. Lett. 2000, 2, 1903-1905. 

Cleomeolide (91) is an unusual bicyclic diterpenoid obtained156 from Cleome viscosa (Capparaceae). The Basidiomycetes contain a number of unusual terpenoid metabolites such as the cyathins. These have now been thoroughly reviewed.157... 

An unusual diterpenoid, cyathin A3 (121). has been isolated from the bird s nest fungus, Cyathus helenae. Its structure, which followed from a careful examination of the n.m.r. spectrum supported by an X-ray analysis, represents a unique cyclization and rearrangement of geranylgeranyl pyrophosphate (122). 

The cyathins are a group of metabolites from the Bird s Nest fungi. Cyathatriol (83), which is related to cyathin A3, together with its mono- and di-acetates, has been isolated from Cyathus earlei. The labelling and coupling patterns produced in 11-O-acetylcyathatriol (85), when it is biosynthesized from [ C]2-... 

Drege, E., Morgant, G. and Desmaele, D. (2005) Asymmetric synthesis of the tricychc core of cyathin diterpenoids via intramolecular Heck reaction. Tetrahedron Lett., 46, 7263-6. 

Neoabietic acid, T32.il Levopimaric acid, T32.il Palustric acid, T32.il Abietic acid, T32.il, T"33, D"4 Pimaric acid, T32.14, T"32 Isopimaric acid, T32.18 Cyathin A2, T 13.7 Isoagatholactone, T 14.2, T"39 Sandaracopimaric acid, T32.18 Trachylobanic acid, T35.6 3-Hydroxy-7-kemp-8-en-6-one, T"37.15 C20H30O3... 

Cyathin diterpenoid model Intramolecular HR of an alkenyl triflate [460[... 

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