Enantioselective First Total Syntheses of 2-(Formylamino)trachyopsane and ent-2-(Isocyano)trachyopsane via a Biomimetic Approach

Abstract

A biomimetic rearrangement of an isotwistane to a tri­cyclo[4.3.1.0^³,8]decane has been employed as the key step for the enantioselective first total syntheses of the marine sesquiterpenes 2-(formylamino)trachyopsane and ent-2-(isocyano)trachyopsanes ascertaining the biogenetic relationship between the marine sesqui­terpenes neopupukeananes and trachyopsanes.

Key words

natural products - marine sesquiterpenes - enantioselective synthesis - biomimetic synthesis - acid-catalysed rearrangement

References and Notes

• 1 Patil AD. Freyer AJ. Reichwein R. Bean MF. Faucette L. Johnson RK. Haltiwanger RC. Eggleston DS. J. Nat. Prod.  1997,  60:  507 
• 2a He HY. Faulkner DJ. Shumsky JS. Hong K. Clardy J. J. Org. Chem.  1989,  54:  2511 
• 2b He HY. Salvi J. Catalos RF. Faulkner DJ. J. Org. Chem.  1992,  57:  3191 
• 3 Okino T. Yoshimura E. Hirota H. Fusetani N. Tetrahedron  1996,  52:  9447 
• 4 Karuso P. Poiner A. Scheuer PJ. J. Org. Chem.  1989,  54:  2095 
• 5 Fusetani N. Wolstenhohne HJ. Matsunaga S. Hirota H. Tetrahedron Lett.  1991,  32:  7291 
• 7 Srikrishna A. Gharpure SJ. Chem. Commun.  1998,  1589 
• 9 Chen HG. Goel OP. Kesten S. Knobelsdorf J. Tetrahedron Lett.  1996,  37:  8129 

6

So far there is no report in the literature on the total synthesis or model studies of any racemic or optically active trachyopsanes.

8

The rearrangement was attempted with BF₃˙OEt₂, BF₃˙OEt₂ in the presence of TFA, TFA, MeSO₂OH, and concentrated H₂SO₄; in all these experiments either starting material recovered or a complex mixture was produced. Reaction with formic acid generated the formate ester of the alcohol 17, whereas PTSA (1 equiv) in MeCN produced a mixture of the acetate and tosylates of the alcohol 17 along with the rearranged product 18. Significant amount (50-60%) of rearranged product 18 was formed when the reaction was carried out with PTSA (1 equiv) in refluxing benzene.