Organometallic derivatives of natural products: dicobalt hexacarbonyl complexes of geranyl-alkynes

Abstract

Treatment of methyl geranyl ether with diiron nonacarbonyl leads to hydrogen migration to form previously unknown E and Z 1-methoxy-3,7-dimethyl-1,6-octadiene in low yield. Sodium propargyl alkoxide and geranyl bromide yield propargyl geranyl ether, 13; subsequent reaction with dicobalt octacarbonyl and then bis(diphenylphosphino)methane furnishes the corresponding alkyne–Co₂(CO)₄(dppm) tetrahedral cluster, 16. Reaction of geranylacetone with phenylethynyl-lithium, and then with Co₂(CO)₈, forms (1-phenyl-3,7,11-trimethyldodeca-6,10-dien-1-yn-3-ol)Co₂(CO)₆, 19. The carbynyltricobaltnonacarbonyl clusters RC(O)CCo₃(CO)₉, where R = geranyl, 23, or farnesyl, 25, are preparable in very good yield either by reaction of the appropriate alcohol with trichloroacetyl chloride and then Co₂(CO)₈, or by reaction with the metal-stabilized acylium ion [Co₃(CO)₉CCO]⁺, 24. Potential use of these (η²-alkyne)dicobalt complexes in Pauson–Khand or Nicholas cyclizations is discussed.