Γ‐Lakton‐cis‐anellierung an Δ²‐ und Δ³‐ Cholesten

Abstract

y-Lactone-cis-annulation to Az-and As-Cholestene. -Summary. From 4 2 -and 4 3 -cholestene the y-lactones lla, 11 b, 12a, and 12b are synthesized through the dibromocarbene adducts 3 and 4, the bromohydrines 5 and 6, the oxaspiropentanes 7 and 8, and the cyclobutanones 9a, 9b and 10a, lob, respectively. The W-NMR.-spectra of 1-8 and 11 as well as the 0RD.-spectra of the cyclobutanones 9 and 10 are reported.

Fluorinated β‐Diketones in Reactions with Diazocyclopropane Generated in situ

“…Scheme 3 Oxaspiropentanes are very important intermediates in organic synthesis. [36,37] Their versatility as synthetic blocks is clearly demonstrated by their capability to react with nucleophiles such as PhSeNa [38] and bases [39Ϫ41] such as R 2 NLi to give cyclopropanols, and to undergo ring-expansion to cyclobutanones on treatment with acidic reagents such as protonic acids, lithium or europium salts [39,42Ϫ44] or by thermal treatment. [45,46] It has been found that Grignard reagent-induced ring-expansion of oxaspiropentanes to cyclobutanols occurs through the intermediacy of a cyclobutanone, [47Ϫ48] and it has also been noted that the interaction of diazocyclopropane (3) generated in situ with the carbonyl groups of trispirodecanone [21] and of some ketosteroids [22,23] affords the corresponding cyclobutanones as a result of the isomerization of unstable oxaspiropentane intermediates.…”

“…H NMR (200 MHz, CDCl 3 , 25°C): δ ϭ 1.12 (m, 4 C, 4-H and 5-H), 1.77 (m, 12 H, Ad), 2.08 (m, 3 H, Ad), 2.69 (dd, 2 J ϭ 17.5, J ϭ 1.8 Hz, 1 H) and 3.53 (d, 2 J ϭ 17.5 Hz, 1 H, CH 2 ), 5.85 (t, J H,F ϭ 55.5 Hz, 1 H, CHF 2 ) ppm. 13 C NMR (50.3 MHz, CDCl 3 ): δ ϭ 1.9 and 2.7 (both s, C-4 and C-5), 27.8, 36.4, 37.9 and 46.7 (all s, Ad),36.6 (s, CH 2 ), 60.8 (dd, 2 J CF ϭ 26.5, 29.0 Hz, C-2), 61.5 (dd, 3 J CF ϭ 3.0 and 6.0, C-3), 114.9 (dd, J C,F ϭ 242 and 244 Hz, CHF 2 ), 206.1 (s, CO) ppm.19 F NMR (188.3 MHz, CDCl 3 , CCl 3 F): δ ϭ Ϫ124.7 and Ϫ127.3 (dd, J FF ϭ 294, J H,F ϭ 55.5 Hz, CHF 2 ) ppm. EIMS (70 eV): m/z (%) ϭ 296 (10) [M] ϩ , 277 (1) [M Ϫ F] ϩ , 256 (8), 245 (83), 135 (100), 93(19), 79(21).…”

The Chemistry of Cyclopropanols

“…A flexible way to obtain alkenylcyclopropanols is nucleophilic ring opening of the oxirane ring in oxaspiropentanes 141,155 which, in turn, may be prepared by epoxidation of cyclopropylidenes, ,, by nucleophilic addition of 1-lithio-1-bromocyclopropanes to ketones, , or by cyclopropanation of carbonyl compounds with diphenylsulfonium cyclopropylide. ,− Treatment of oxaspiropentanes 92 with lithium diethylamide led to unstable 1-vinylcyclopropanol alcoholates 93 , which were directly derivatized with trimethylchlorosilane to give 1-alkenylcyclopropanol silyl ethers 94 in good yields (Scheme ) 44 …”

Unexpected Stereochemistry in the Lithium Salt Catalyzed Ring Expansion of Nonracemic Oxaspiropentanes. Formal Syntheses of (−)-(4R,5R)-Muricatacin and the Pheromone (R)-Japonilure

“…Oxaspiropentanes constitute an important class of compounds in organic synthesis , and are usually prepared by peracid oxidation of methylenecyclopropanes, − through nucleophilic addition of 1-bromo-1-lithio-cyclopropanes to ketones at low temperatures − or through reaction of sulfur ylides with carbonyl compounds. − They are extremely versatile compounds, as clearly demonstrated by their capability to react with nucleophiles and bases 15-17,19 to give cyclopropanols and to undergo ring expansion to cyclobutanones by reaction with acidic reagents such as protonic acids, lithium or europium salts 1,2,5,6,15-18,20,21 or by thermal treatment. , …”