Dominic C. Yang

Cycloadditions and annulations of transition metal carbene complexes

Abstract The synthetic aspects of several reactions from the multifaceted chemistry of Fischer carbene complexes are examined. Their benzannulation reactions with acetylenes are utilized in the synthesis of anthracyclinones via two approaches which differ by beginning at opposite ends of the molecule with either an aryl or an alkenyl substituted chromium carbene complex. The latter has been employed in a formal synthesis of daunomycinone. The Diels-Alder reactions of α,β-acetylenic chromium carbene complexes provide for a facile entry into substituted cyclohexenyl chromium carbene complexes that are subsequently employed in benzannulation reactions. These tandem cycloaddition/annulation reactions are incorporated into model studies for the synthesis of anthracyclinones and wentilactone A. Their potential is also demonstrated for coupling to yet a third reaction of organochromium compounds ; aromatic nucleophilic substitutions on arene chromium tricarbonyl complexes. The annulations of β,β-disubstituted alkenyl complexes provides for a regio- and stereoselective synthesis of 2,4-cyclohexadienones under neutral conditions at near ambient temperatures.

Cyclopropanations and cycloadditions of transition metal carbene complexes

The first examples of the cyclopropanation of 1,3-dienes with transition metal carbene complexes is reported for the heteroatom-stablized pentacarbonyl complexes of the group 6 metals. The reaction of the chromium phenylmethoxymethylene complex 36 with Danishefskys diene gives varying amounts of cyclopro- panes and metathesis products whose distribution is carbon monoxide dependent. The reactions of the cyclo- hexenylmethoxymethylene complexes is metal dependent. The chromium complex 12a gives a chemoselective reaction with Danishefskys diene resulting in the formation of cyclopropanes, whereas, the same reaction of the tungsten complex 12b chemoselectively gives Diels-Alder cycloadducts. Some cyclopropanation reactions of the phenylmethoxymethylene complex 36 with silyl enol ethers and enamines are also presented.

Syntheses of Dibenzo[h,rst]Pentaphene and Naphtho[1,2,3,4-rst]Pentaphen

Abstract Syntheses of the fused heptacyclic polyarenes dibenzo[h,rst]pentaphene (1), naphthol[1,2,3,4-rst]pentaphene (2), and the pentacyclic polyarene 8H-naphth[1,2,3-de]anthracene (8), of interest in carcinogenesis research, are described.

Synthesis of allenes via reduction of acetylenic tosylhydrazones

The reduction of tosylhydrazones of conjugated acetylenic ketones occurs with migration of one of the acetylenic bonds, providing a mild synthesis of allenes.