Synthesis ABCD-ring

Another natural product synthesis using a metathesis as the key step has been reported to generate the ABCD ring system 133 of manzamine A. A multistep... 

Scheme 2.30. Synthesis of the ABCD-ring skeleton of (+)-lactonamycin (2-132).

Magnus, P. Mansl, T.E. (1999) Synthesis of the ABCD-rings ofthe insecticidal indole alkaloid nodulisporic acid. Tetrahedrcm Lett., 40,6909-12. 

Synthesis of ABCD-ring Fragment by Mori and Co-workers... 

Nicolaou, K.C., Qian, W.Y., Bernal, F, Uesaka, N., Pihko, PM., andHinrichs, J. 2001b. Synthesis ofthe ABCD ring system of azaspiracid. Angew Chem IntEd 40(21) 4068 071. 

The First Synthesis of the ABCD Ring System of Manzamine A. Construction of the Macrocyclic Ring D. Borer, B. C. Deerenberg, S. Bieraugel H. Pandit, U. K. Tetrahedron Lett. 1994, 35, 3191. 

Henderson, D.A., Collier, P.N., Pave, G. et al. (2006) Studies on the total synthesis of lactonamycin construction of model ABCD ring systems. The Journal of Organic Chemistry, 71, 2434-2444. 

Sasaki, M. et al., A general method for convergent synthesis of polycyclic ethers based on Suzuki cross-coupling Concise synthesis of the ABCD ring system of ciguatoxin, Org. Lett., 1, 1075, 1999. 

Scheme 22 Synthesis of the ABCD-ring system associated with aspidospeimidine (228)...

The synthesis of baccatin III presents a formidable challenge, because the molecule contains an unusual and distorted ABCD ring... 

Volhardt s tZZ-estrone synthesis was the first application of a transition-metal-catalyzed [2 -1- 2 -I- 2] alkyne cyclotrimerization in natural product synthesis, and the overall beauty of the synthetic sequence is still appealing [4,5]. Undoubtedly, this brilliant synthesis is a classic in its field. Following a D ABCD ring formation approach, the tetracyclic core of estrone was produced in a single reaction step by profiting from a reaction cascade that started with a cobalt-mediated crossed [2 + 2 + 2] alkyne cycloaddifion, which was followed by a benzocyclobutane to o-quinodimethane rearrangement, and was finalized by an intramolecular Diels-Alder reaction (Scheme 7.2). 

ABCD-ring of cortistatins dr = 5 1 SCHEME 12.56 Synthesis of ABCD-ring of cortistatins. 

The first transannular [4 + 3] cycloaddition was reported by Craft and Gung in the synthesis of the oxabicyclo[3.2.1] octene ABCD ring system of cortistatins." The reaction... 

Craft DT, Gung BW. The first transannular [4+3] cycloaddition reaction synthesis of the ABCD ring structure of cortistatins. Tetrahedron Lett. 2008 49 5931-5934. 

Maeda, K., Oishi, T, Oguri, H., and Hirama, M. (1999) Convergent synthesis of the ABCDE ring framework of ciguatoxin. Chem. Commun., 1063-1064. 

Sasaki, M., Ishikawa, M., Fuwa, H., and Tachibana, K. (2002) A general strategy for the convergent synthesis of fused polycyclic ethers via B-alkyl Suzuki coupling synthesis of the ABCD ring fragment of ciguatoxins. Tetrahedron, 58,1889-1911. 

Borer, B.C., Deerenberg, S., Bieraugel, H., and Pandit, U.K. (1994) The first synthesis of the ABCD ring system of manzamine A. Constmction of the macrocyclic ring D. Tetrahedron Lett., 35, 3191-3194. 

Ishikawa, Y. and Nishiyama, S. (2004) Synthesis of the ABCD ring system of azaspiradd, a marine poison from Mytilus edulis. Heterocycles, 63, 885-893. 

A second synthesis of cobyric acid (14) involves photochemical ring closure of an A—D secocorrinoid. Thus, the Diels-Alder reaction between butadiene and /n j -3-methyl-4-oxopentenoic acid was used as starting point for all four ring A—D synthons (15—18). These were combined in the order B + C — BC + D — BCD + A — ABCD. The resultant cadmium complex (19) was photocyclized in buffered acetic acid to give the metal-free corrinoid (20). A number of steps were involved in converting this material to cobyric acid (14). 

The selectivity for two-alkyne annulation can be increased by involving an intramolecular tethering of the carbene complex to both alkynes. This was accomplished by the synthesis of aryl-diynecarbene complexes 115 and 116 from the triynylcarbene complexes 113 and 114, respectively, and Danishefsky s diene in a Diels-Alder reaction [70a]. The diene adds chemoselectively to the triple bond next to the electrophilic carbene carbon. The thermally induced two-alkyne annulation of the complexes 115 and 116 was performed in benzene and yielded the steroid ring systems 117 and 118 (Scheme 51). This tandem Diels-Alder/two-alkyne annulation, which could also be applied in a one-pot procedure, offers new strategies for steroid synthesis in the class O—>ABCD. 

Several total syntheses of cortisone have been described [25-32]. One of these is the highly stereospecific synthesis of Sarett et al. [30], which is described below and outlined in Scheme 1. This synthesis is of the type C -> BC -> ABC ABCD, where one constructs ring-C at first, followed by conversion to rings BC, then rings ABC, and finally to rings ABCD. 

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