Synthesis of Hydrazulenes via Zr-Promoted Bicyclization of Enynes and Transition Metal-Catalyzed or Radical Cyclization of Alkenyl Iodides. Efficient Synthesis of (±)-7-epi-β-Bulnesene

Applications of stoichiometric organotransition metal complexes in organic synthesis

“…Use of an enyne precursor to cyclisation enabled Negishi to undertake a similar sequence which resulted in the synthesis of (±)-7-epi-β-bulnesene (Scheme 2). 3 Compound 3 was cyclised in a manner analogous to reaction of 1, and the resulting zirconacycle was functionalised with an isocyanide and then iodine to produce (after acid hydroysis) vinyl iodide 4. This was subsequently transformed into the target molecule in four steps.…”

“…Aldol reaction of the aforementioned enolate was also diastereoselective and this chemistry gave compound 26 in 88% ee and as a single diastereoisomer (Scheme 19). 3 -Complexes of titanium η 3 -Complexes of titanium have been used to good effect in the synthesis of stereochemically defined acyclic 1,3-diols using the aldol reaction (Scheme 20). 46 The allyltitanium species 27 was prepared from the corresponding diene and then treated with a series of aldehydes.…”

Natural sesquiterpenoids

“…107 The sesquiterpene furanoguaian-4-ene 292 has been isolated from the Caribbean gorgonian coral Pseudopterogorgia americana. 279 Racemic syntheses of 7-epi-b-bulnesene 280 and dictammol 281 have been reported. A facile conversion of a methyl group of guaiazulene into a formyl group has been described.…”

Ready Access to Bicyclo[5.3.0]decan-1-ones and to Bicyclo[6.3.0]undecan-1-ones by Intramolecular Pauson−Khand Reactions Using a Temporary Sulfur Bridge

“…Some of the most successful strategies that have been devised for the construction of these molecular systems are based on transition metal-mediated cyclization processes. − However, the Pauson−Khand reaction, which stands out as a very powerful method for the one-step construction of cyclopentenones with high stereo- and regioselectivity, and which has been widely employed in the synthesis of natural products, either in racemic or in enantiomerically pure form, has been up to now largely unsuccessful in the preparation of perhydroazulene or perhydrocyclopentacyclooctene systems. Thus, the intermolecular version of the reaction is practically restricted to the use of strained, reactive olefins and, in fact, both cycloheptene and cyclooctene react only at high temperatures with the dicobalt hexacarbonyl complexes of terminal alkynes, affording the corresponding bicyclic enones in low yields. , On the other hand, the intramolecular version of the Pauson−Khand reaction has seldom been used for the construction of bicyclic systems other than bicyclo[3.3.0]oct-1-en-3-ones and bicyclo[4.3.0]non-1(9)-en-8-ones.…”