Three-carbon annulations

There exists also a synthesis of cyclopentadecanone (VII/81) and ( )-mus-cone, based on a three-carbon annulation of cyclic ketones followed by the regioselective radical cleavage of the zero bridge of the so formed bicyclic system [44], The synthesis of cyclopentadecanone is summarized in Scheme VII/16. The cyclization of VII/78 to the bicyclic alcohol VII/79 proceeds best (94 % yield) with samarium diiodide in the presence of hexamethylphosphoric acid triamide and tetrahydrofuran [45], The oxidative cleavage of VII/79 to the ring expanded product VII/80, was performed by treatment with mercury(II)-oxide and iodine in benzene, followed by irradiation with a 100 Watt high pressure mercury arc. Tributyltinhydride made the de-iodination possible. 

The intramolecular carbene addition from the diazoketone (58), leading to (59), is a key step in a new synthesis of hirsutene (60) described by Hudlicky and co-workers (Scheme 9). In a second new approach to hirsutene, Greene has applied his so-called three-carbon annulation procedure, based on the diazomethane-induced ring expansion of a-chlorobutanones, announced last year (Scheme 9). 

In contrast to cyclopropyl ketones that function as three-carbon annulation units, cyclopropyl imines can participate in annulation as five-atom units. Carbonylative [5+1] annulation of cyclopropyl imine 126 was catalyzed by metal carbonyl complexes to afford six-membered unsaturated lactam 127 (Scheme 2.84) [62,138]. 

Fussed Five-monbered Rings.—comprehensive review of the chemistry of 4-acetoxycyclopent-2-en-l-one includes some approaches to fused cyclopent-anoids. The vinylcyclopropane rearrangement has been extended into a novel three-carbon annulation reaction by using the (1-trimethylsiIylcycIopropyI) cyclohexene (60), which gives 80% of the rearranged product (61). Obviously,... 

---