Control of the Regio‐ and Diastereoselectivity for the Preparation of Highly Functionalized Terpenic Cyclopentanes through Radical Cyclization

Abstract

The titanocene-mediated cyclization of suitably functionalized acyclic C10 epoxy-polyprenes leads, with moderate stereoselectivity, to high yields of functionalized terpenic cyclopentanes with three contiguous stereogenic centers. These highly functionalized cyclopentanes are useful intermediates for the synthesis of several natural compounds that

Easy Access to a Cyclic Key Intermediate for the Synthesis of Trisporic Acids and Related Compounds

“…Cp 2 TiCl 2 can be regenerated by means of the 2,4,6-collidine/TMSCl system either from the Cp 2 Ti(IV)Cl(OAc) generated in the -OAc elimination step or from the titanium alkoxide of VIII. It should be pointed out that the Ti(III)-mediated radical cyclization reactions employing substrates without secondary acetate groups at C-4 lead regioselectively to exocyclic double bonds (Scheme 5) [45,[47][48][49][50]. In contrast, in this study it has been proven that it is possible to change selectively the direction of the formation of the olefin by using a suitable leaving group having in mind the affinity for the oxygen of the Ti atom.…”

“…Finally, the acyclic epoxide 8, which also corresponds to the intermediate III of Scheme 1, was cyclized following the Ti(III)-mediated methodology [39,[45][46][47][48][49][50]. In this case catalytic conditions [51] were employed, involving 0.3 equivalents of Ti(III) and 8.0 equivalents of Mn in THF (0.1 M), with 2,4,6-collidine/TMSCl as regenerating system.…”

Regioselective Cleavage of Electron‐Rich Double Bonds in Dienes to Carbonyl Compounds with [Fe(OTf)2(mix‐BPBP)] and a Combination of H2O2 and NaIO4

“…Here, oxidation occurs selectively at the C=C double bond remote from chloride with 65 % yield (Table 2, entry 4). Notably, such epoxyolefins are valuable substrates for radical‐type 5‐ exo ‐cyclizations 31…”

Ti‐Mediated Efficient Reductive Dehalogenation of Carbon–Halogen Bonds

“…( E )‐9‐Chloro‐6,10‐dimethylundeca‐5,10‐dien‐2‐one (4′) : Following the general procedure for allylic chlorination, 4′ was obtained after subjecting the resulting reaction crude to purification by column chromatography (hexane/ t BuOMe, 3:1) on silica gel. 1 H NMR (CDCl 3 , 300 MHz): δ =5.07 (t, J =7.1 Hz, 1 H), 4.94 (s, 1 H), 4.84 (s, 1 H), 4.27 (t, J =7.0 Hz, 1 H), 2.41 (t, J =7.3 Hz, 2 H), 2.21 (q, J =7.2 Hz, 2 H), 2.08 (s, 3 H), 1.77–2.05 (m, 4 H), 1.75 (s, 3 H), 1.56 ppm (s, 3 H); 13 C NMR (CDCl 3 , 75 MHz): δ =208.3, 144.3, 134.7, 123.8, 114.1, 66.2, 43.5, 36.6, 34.7, 29.9, 22.4, 17.0, 15.9 ppm; HRFABMS ( m / z ): [ M +H] + calcd.…”