Rearrangement Approaches to Cyclic Skeletons. IV. The Total Synthesis of (+/-)-Pinguisone and (+/-)-Deoxopinguisone Based on Photochemical Acyl Migration of a Bicyclonon-6-en-2-one

Article abstract of DOI:10.1246/bcsj.59.2521

The total synthesis of (+/-)-Pinguisone (2) and (/-)-deoxopinguisone (3), <5-6> fused ring sesquiterpenes, has been achieved starting from 1-methoxy-3,4,5-trimethylbenzene. 1-Methoxy-4,5,endo-8-trimethylbicyclo<2.2.2>non-5-en-2-one (9) was prepared selectively via facial selective Diels-Alder reaction of the diene derived from the benzene and 2-chloroacrylonitrile.Ring enlargement of 9 using (CH3)3SiCHN2 and BF3 etherate gave the corresponding bicyclo<3.2.2>oct-en-2-one (8).The photochemical <1,3> acyl migration of 8 gave the <5-6> fused-ring compound (7).The fourth methyl was introduced selectively by the conjugate addition of (CH3)2CuLi to the spironon-8-ene-3,2'-<1,3>dioxolan>-7-one prepared from 7.Each furan ring of 2 and 3 was constructed via the corresponding butenolide derived from the γ-keto acid by acid-catalyzed dehydration.