Iridoids: An efficient conversion of (−)-catalpol into (−)-specionin

Total synthesis of (±)-specionin

“…Purification by flash chromatography [light petroleum-ethyl acetate (1 : 2)] provided diol 18 (77 mg, 64% from the epoxide lla), v,,,/cm-' 3400, 3075, 3050, 1500 and 700; 6,(60 MHz) 1.62.25 (3 H, m), 2.9-3.45 (2 H, m), 3.5-3.8 (1 H, m), 3.85-4.3 (4 H, m), 4.354.9 (5 H, m), 5. 5 (1 H, m, 3-H) and 7.3 (10 H, m); m/z (CH,, CI) 367 ([M + H I + , 2.079, 349 (2), 331 (2), 181 (30) and 91 (100) (characterised further as its monoacetate 20a-see below). A solution of the above monoacetate 19a (50 mg, 0.12 mmol), vanadyl acetylacetonate (1 0 mg) and tert-butyl hydroperoxide (5.36 mol dm-, in dichloromethane; 46 mm3, 0.25 mmol) in dry dichloromethane (8 cm3) was heated at reflux for 2 h. The solution was then diluted with dichloromethane (25 cm3), washed successively with saturated aq.…”

“…In the earlier work we had also devised a general method for introducing the C-6 hydroxy group via an epoxidation-alcohol oxidationepoxide-opening sequence. With the stereoisomers 5 and 6a available separately we thought that each of them could be transformed into a C-6p epoxide; compound 7 being formed by directed epoxidation from 5 and compound 8a being formed by sterically con trolled epoxidation of an alcohol derivative of compound 6a. Thus our first objective was to prepare the alcohol 9 with the correct C-6p hydroxy-group stereochemistry which could then be used to direct epoxidation of the C-7, C-8 alkene (Scheme 2).…”

Spruce budworm (Choristoneura fumiferana) antifeedants 3. Structure–activity relationship among some angularly functionalized decalin compounds

“…Chang and Nakanishi (5) have isolated the iridoid specionin (3), from leaves of Catalpa speciosa and found it to be an effective antifeedant against the spruce budworm. Specionin has recently been synthesized (6,7).…”