1. All glassware contained 24/40 joints and was either flame-dried or oven-dried (110 °C) overnight prior to use, if not otherwise noted. All reaction steps and reagents were performed under a partial positive nitrogen gas atmosphere using a nitrogen gas line connected to an external mineral oil bubbler.
2. Copper(I)bromide dimethylsulfide (99%, Acros Organics), 4-penten-1-ol (99%, Acros Organics), and boric acid (>95%, Fisher Scientific, Reagent grade) were used as received. 2-Cyclohexene-1-one (>95%, Sigma-Aldrich) was freshly distilled (76 °C, 37 mmHg) prior to use. The submitters mentioned boric acid was either used as received or recrystallized two times from boiling deionized water and dried under high vacuum.2 No appreciable difference in overall yield or reactivity was observed by the checkers using recrystallized vs. non-recrystallized boric acid.
3. Toluene and tetrahydrofuran were dried using a solvent purification system manufactured by SG Water U.S.A., LLC. Column chromatography solvents EtOAc and hexanes were used as received. Diethyl ether (ACS grade) and NH4OH (ACS grade) were used as received.
4. A Pyrex® crystallization dish with a diameter of 15.0 cm and a height of 7.0 cm was used.
5. A mercury thermometer with a range of -20 to 110 °C was used.
6. The submitter followed the reaction progress by removing an aliquot (0.15 mL) of the reaction mixture after cooling to 22-23 °C and directly transferring it to an NMR tube for 1H NMR analysis. The analysis showed ~85% conversion of the reagents to a single borate species: 1H NMR (300 MHz, dry CDCl3) δ: 1.77-1.84 (m, 2 H), 2.26-2.29 (m, 2 H), 3.94-3.99 (m, 2 H), 5.11-5.22 (m, 2 H), 5.92-6.06 (m, 1 H). This reaction has been performed under the same reaction conditions on a 1.0-mmol scale in both benzene and toluene at reflux furnishing the crude tripent-4-enyl borate, after removal of the reaction solvent via distillation and high vacuum, with 95-98% mass recoveries and in nearly identical purity to that of this reaction as analyzed by 1H NMR.
7. Cp2ZrHCl was prepared employing a method reported by Buchwald and co-workers.3 The activity of this reagent was measured by a convenient 1H NMR assay: To a suspension of Cp2ZrHCl (0.05 mmol, 12.9 mg, 1.0 equiv) in dry CH2Cl2 (0.50 mL) was immediately added tert-butyldiphenyl(prop-2-ynyloxy)silane (0.05 mmol, 14.7 mg, 1.0 equiv). The resulting homogeneous pale yellow reaction mixture was stirred at room temperature for 15 min, quenched by the addition of saturated NH4Cl solution (0.50 mL), and stirred for 5 min. The organic solvent layer was separated, filtered through a 1" plug of Celite contained in a disposable 5 ¾" Pasteur pipette, washed with additional CH2Cl2 (1.5 mL) and concentrated by rotary evaporation (40 °C). The resulting white solids were dried under high vacuum for 30 min. This procedure was repeated three times on three different samples for each new batch of Cp2ZrHCl. The percent conversion for each reaction was then determined via a 1H NMR (300 MHz, CDCl3) analysis by comparison of the integrated areas for the alkyne CH2O peak at δ 4.32 (d, J = 2.4 Hz, 2 H) to the alkene CH2O peak at δ 4.22 (dt, J = 4.5, 2.0 Hz, 2 H). Typical values for the average % conversion among the three experiments were found to be 73-83%. The numerical value for the average % conversion for a particular batch of Cp2ZrHCl was used to calculate the number of equivalents of Cp2ZrHCl (by mass) used in these hydrozirconations, ensuring that only a slight excess of Cp2ZrHCl (3.1 equiv) was used in each experiment. Sample calculation: average % conversion = 78%; 3.1 active equiv of Cp2ZrHCl = (X equiv of Cp2ZrHCl) x 0.78 => X = 4.0 equiv of Cp2ZrHCl.
8. The septum in Neck 3 was removed with the apparatus under a positive pressure of nitrogen gas atmosphere and then immediately replaced after the addition of reagent.
9. No exotherm was noted upon the addition of Cp2ZrHCl to 1. The submitter mentioned that this observation stands in contrast to the reaction of 4-penten-1-ol (2.07 mL, 20.0 mmol, 1.0 equiv) with Cp2ZrHCl (11.1 g, 43.0 mmol, 2.15 equiv) in THF (50 mL) at 25 °C (internal temperature) which was found to be exothermic (reaction temperature increasing to 34 °C) and accompanied by a vigorous (H2) gas release, which persisted for 2 min, as a result of the deprotonation of 4-penten-1-ol with Cp2ZrHCl.
10. The submitter followed the reaction progress by 1H NMR (300 MHz, CDCl3) analysis of aliquots (0.10 mL) of the reaction mixture. An approximate % conversion for the hydrozirconation reaction can be obtained by comparing the integrated areas for the tripent-4-enyl borate olefin proton resonance δ 4.97-5.10 (m, CH2) vs. the newly formed tris[5-(biscyclopentadienyl)zirconium(IV)chloride)pentyl] borate methylene proton resonance δ 0.90-0.97 (m, 2H). This analysis gave 90%, 97% and 96% conversions for reactions run on 7%, 50% and 100% scales, respectively. Thin layer chromatography (Whatman®, aluminum backed, 250 µm thickness) analysis using a 1:1 mixture of hexanes:EtOAc as the eluent and a p-anisaldehyde solution (2.5 mL of p-anisaldehyde, 2.0 mL of AcOH, and 3.5 mL of conc. H2SO4 in 100 mL of 95% EtOH) for visualization showed a dark green/brown spot with an Rf = 0.03 for the hydrozirconation product.
11. The submitter mentioned that a mild exotherm was noted upon the addition of 2-cyclohexen-1-one to the reaction mixture with the reaction temperature rising from 23 °C to 25 °C. This exothermic reaction is quite possibly the result of the reaction of any excess Cp2ZrHCl with 2-cyclohexen-1-one, since it was found that an exothermic reaction took place upon the addition of Cp2ZrHCl (134.0 mg, 0.52 mmol, 1.0 equiv) to a solution of 2-cyclohexen-1-one (47.4 μL, 0.52 mmol, 1.0 equiv) in THF (3.0 mL) with the reaction temperature rising from 25 °C to 32 °C. This reaction provided 2-cyclohexen-1-ol in good conversion by crude 1HNMR (300 MHz, CDCl3) analysis and demonstrates the importance of using a slight excess of 2-cyclohexen-1-one in the above protocol.
12. The reaction mixture slowly re-cooled to 23 °C over 1.5 h.
13. The black color is a result of precipitation of copper(0) from the reaction mixture.
14. The submitter reported that the reaction progress was monitored by thin layer chromatography (Whatman® aluminum backed, 250 µm thickness) using a 1:1 mixture of hexanes:EtOAc as the eluent and a p-anisaldehyde solution for visualization. After 2 h reaction time, the conversion of 2-cyclohexen-1-one (Rf = 0.72) to the product 3-(5-hydroxypentyl)cyclohexan-1-one (Rf = 0.43) ceased after near complete consumption of 2-cyclohexen-1-one.
15. Anhydrous sodium sulfate (EMD, ACS grade, granular powder) was used as received.
16. A 3.0 mg sample of the crude mixture was dissolved in CH2Cl2 (1.0 mL) and analyzed by GC (HP-5ms agilent 30 m x 0.25 mm x 0.25 µm, helium flow 1.0 mL/min, temperature gradient 110 °C to 280 °C at 30 °C/min, FID detector). GC analysis showed a >96:4 ratio of the desired product 3-(5-hydroxypentanyl)cyclohexanone (3) (retention time of 4.74 min) to the side product 3-(5-hydroxypentan-2-yl)cyclohexanone (4).
17. SiO2 40-63 µm D (Silicycle, Quebec City, Canada) was used.
18. The submitter noted that the yellow band was found to contain a complex mixture of reaction byproducts including 2-cyclohen-1-ol, 4-penten-1-ol and 1-pentanol as determined by 1H NMR (300 MHz, CDCl3) analysis.
19. Column chromatography conditions to completely separate 3-(5-hydroxypentyl)cyclohexan-1-one and the minor regioisomer 3-(5-hydroxypentan-2-yl)cyclohexanone have not been identified. The chromatography conditions reported above allow for a partial separation of the two reaction products in which the last fractions of 3-(5-hydroxypentyl)cyclohexan-1-one are enriched with the byproduct 3-(5-hydroxypentan-2-yl)cyclohexanone. Collection, combination and concentration of column fractions 53-60 led to an enriched sample (90 mg) containing a 94:6 mixture of 3-(5-hydroxypentyl)cyclohexan-1-one (3): 3-(5-hydroxypentan-2-yl)cyclohexanone (4), as determined by GC (conditions in Note 16) and 1H NMR pdf(400 MHz, CDCl3) analysis. The isomer 3-(5-hydroxypentan-2-yl)cyclohexanone (4) can be identified by 1H NMR (400 MHz, CDCl3) as a result of its characteristic methyl peak at δ 0.89 (d, J = 6.8 Hz, 3 H, -CH3).
20. The submitters reported that attempts to optimize this reaction included: (A) Reacting 4-penten-1-ol (0.269 mL, 2.58 mmol) with 2.0 equivalents of Cp2ZrHCl (1.33 g, 5.16 mmol) at 5 °C in THF (10 mL) either by the addition of 4-penten-1-ol to a suspension of Cp2ZrHCl (2.0 equiv) in THF at 5 °C followed by warming to 20 °C over 20 min or by sequentially reacting Cp2ZrHCl (1.0 equiv) with 4-penten-1-ol (1.0 equiv) at 5 °C and then warming the mixture to 20 °C over 20 min before adding a second equivalent of Cp2ZrHCl. The optimized procedure was found to give a cleaner hydrozirconation reaction product by 1H NMR (300 MHz, CDCl3) analysis. (B) The reaction mixtures were heated to 40 °C for 15-20 min to effect the hydrozirconation reaction, followed by cooling to 25 °C. (C) To the alkyl zirconocene solutions were added 2-cyclohexen-1-one (0.255 mL, 2.58 mmol, 1.0 equiv) followed by CuBr●Me2S (53.5 mg, 0.258 mmol, 1.0 equiv) at 25 °C and the resulting brown mixtures were heated to 40 °C for 30 min to effect the transmetallation/conjugate addition reaction. Finally, these reactions were quenched with NH4OH (14.8 M, 50 mL). While these reaction variants successfully produced 3-(5-hydroxypentyl)cyclohexan-1-one in comparable yields (60-70%, 283-337 mg), the isolated products were found to be contaminated with ca. 8-10% of the 3-(5-hydroxypentan-2-yl)cyclohexanone byproduct (4).
21. The product isolated in fractions 13-52 was found to be 97.6% pure by GC (conditions in Note 16) and contain 0.8% of 3-(5-hydroxypentan-2-yl)cyclohexanone. The product has the following characteristic physicochemical properties: 1H NMR pdf(400 MHz, CDCl3) δ: 1.23-1.39 (m, 7 H), 1.49-1.69 (m, 3 H), 1.68-1.80 (m, 2 H), 1.81-2.08 (m, 3 H), 2.18-2.42 (m, 3 H), 3.60 (t, J = 6.6 Hz, 2 H); 13C NMR pdf(100 MHz, CDCl3) δ: 25.4, 25.9, 26.6, 31.4, 32.7, 36.6, 39.1, 41.6, 48.3, 62.9, 212.4; IR (neat) 3412, 2927, 2856, 1704, 1447, 1421, 1346, 1313, 1279, 1053 cm-1; ESI-MS m/z 185 (24), 207 (100); HRMS (ESI) m/z calcd for C11H21O2 [M+H]+• 185.1536, found 185.1536. A 2.0 g sample was subjected to bulb-to-bulb distillation (150-151 °C/4.0 mmHg) affording 0.957 g (48% recovery) of the product as a clear oil. Anal Calcd for C11H20O2: C, 71.70; H, 10.94; O, 17.36; Found: C, 71.53, H, 11.10.
22. A reaction checked at half-scale provided 2.69 g (68%) of the product. The submitters report that reactions run on 7% and 50% scales produced the product under identical reaction/workup conditions in 65% yield for both reactions with measured GC purities of ≥98% (conditions in Note 16).