Palladium-catalyzed 1,3-oxygen-to-carbon alkyl shifts. A cyclopentanone synthesis

Abstract

The mother liquor provided a second crop of crystals, and the resulting mother liquor showed a 59:35 E:Z ratio. Partial spectra: *H NMR (270 MHz, CDC13) 5.83 (bs, 0.06 H), 5.62 (bs, 0.59 H), 5.32 (bs, 0.35 H), 1.44 (s), 1.26 (s), 1.11 (s); 13C NMR (67.9 MHz, PhH-d6) 22.5 (q), 21.1 (q), 15.8 (q). Method B from 20. To a stirred solution of acetate 20 (85.1 mg, 0.23 mmol) in 1.1 mL of dry Me2SO (previously deoxygenated by flushing with argon) at 25 °C under argon was cautiously added NaH (5.2 mg, 0.22 mmol). The mixture was stirred for 2 h to give a clear, orangeyellow solution. Catalyst 29 (12.8 mg, 0.014 mmol) was added, and the mixture was heated to 130 °C over 15 min. After 45 min at 130 °C the deep red-brown solution was cooled to 25 °C, concentrated in vacuo, and filtered through Florisil (5 X 0.5 cm) with EtOAc (20 mL). Concentration in vacuo and preparative TLC purification, using three elutions with 20% acetone in hexane (v/v), yielded the same product as above (35.8 mg, 52%) as an off-white solid, the physical and spectral characteristics of which were identical with those of the material obtained from reaction of the enol ether. The progress of the reaction can be followed by analytical TLC or NMR, and it clearly proceeds through the intermediacy of the enol ether 21.

Alkynes as Synthetic Equivalents of Ketones and Aldehydes: A Hidden Entry into Carbonyl Chemistry

“…When a secondary allylic alcohol [56] is used as opposed to a primary alcohol [57,58], the process becomes more sluggish and gem -dimethyl groups are required (Scheme 16). Addition of an anion-stabilizing group at the terminal carbon renders 5-exo-dig cyclizations of oxygen nucleophiles more efficient [59,60].…”

Cyclizations via Palladium‐Catalyzed Allylic Alkylations [New Synthetic Methods (79)]

“…(44)J to form theeight-and nine-membered rings preferentially or e x c l~s i v e l y . [~~~ 641The preference for eight-membered ring formation in Equation(43) in part derived from the preference for the nucleophile to attack the less substituted terminus of the ally1 system. Equalizing the substitution pattern as in 39 returned the cyclization to six-membered ring formation [Eq.(45)].…”

Carbohydrates to Pyrano-Furanoids: New and Regioselective Palladium-Catalyzed Syntheses of Tetrasubstituted Furanoids from Carbohydrate Scaffolds

“…of the dianion of diethoxycarbonyl acetone (4) (formed at 0 °C using 2.2 equiv. of N aH sus pended in THF) in the presence of 5 mol-% of (Ph3P)4Pd and 10 mol-% of Ph3P, delivered fu- anion is not coordinated to palladium, this would allow C-alkylation to take place to deliver the cyclopentanoid IV through 5-enolexo-exo-trig ring closure [10]. It seems that, stereoelectronic effects prevent such a cyclization (carbo-palladation lead ing to IV ), in which the carbon cannot assume co linearity with the jr-metal complex in III.…”