Chamigrene synthesis

Where there is an electron-rich olefinic double bond in the diazoketone as in the 2-substituted 3,4-dihydropyran derivative 47, the intramolecular cyclopropanation produces oxatricyclic ketones, e.g. 48 (equation 57)86 87. Rhodium(II) acetate is the catalyst of choice for this transformation. An interesting application of this method is found in a stereoselective synthesis of ( )-/ -chamigrene 49 (equation 5S)88. 

Spiroannelatwn of phenolic a-diazoketones (8, 118-119). The Cu(I) decomposition of the phenolic a-diazo ketone 1 has been used for a synthesis of a-chamigrene (3). ... 

Full details of an earlier synthesis of chamigrene (161) have been published.95 Further work on the components of the red alga Laurencia nipponica Yamada has resulted in the isolation and structural elucidation (by Y-ray analysis) of the diol (162)96 and spironippol (164).97 The biogenesis of the latter compound can be viewed in terms of an intramolecular cyclization of the diol (163) derivable from the naturally occurring epoxide of 10-bromo-a-chamigrene. 

Bromocyelization. Wolinsky and Faulkner have published a synthesis of 10-bromo-a-chamigrene (5), the key step of which involves a bromonium ion initiated cyclization of geranylacetone (1) to the vinyl ether (2). This product was... 

An intramolecular cycloaddition of an a diazoketone, a reaction which has featured prominently this year, forms the key step, (250) - (251), in a synthesis of solavetivone. By contrast, intramolecular cycloadditions of car-benoids derived from a-diazoketones have been used in total synthesis of ( )-a-chamigrene and (-)-acorenone B in the latter case, (+)-limonene was used as the chiral precursor. ... 

Wolinsky, L.E. and Eaulkner, D.J. (1976) A biomimetic approach to the synthesis of Laurencia metabolites. Synthesis of 10-bromo-a-chamigrene. y. Org. Chem., 41, 597-600. 

Srikrishna, A. and Babu, R.R. (2008) Total synthesis of ( )- 3-chamigrene and ( )-laurencenone C via Ireland ester Claisen rearrangement and an intramolecular type 11 carbonyl ene reaction sequence. Tetrahedron, 64, 10501-10506. 

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