Crotyl potassium

Crotylboronic esters (2-butenylboronates) are thermally stable and isolable compounds at room temperature and undergo nearly quantitative additions to aldehydes. The required crotylboronic esters may be prepared by reaction of the crotyl potassium reagents derived from cis- or trans-2-butene with n-butyllithium and potassium tert-butoxide followed by addition of the appropriate trialkyl borates. ... 

Homoallyl alcohol (3).6 Metalation of (E)-butene (1.05 equiv.) with n BuLi (1 equiv) and KOtBu (1 equiv.) in THF at -50°C for 15 min. followed by treatment of the (E)-crotyl potassium salt with B(OiPr)3 at -78°C gave, after quenching with 1 N HCI and extraction with Et20 containing 1 equiv. of diisopropyl tartarate, the crotyl boronate 2. A solution of decanal 1 (156 mg, 1 mmol) was added to a toluene solution of 2 (1.1-1.5 equiv.) (0.2 M) at -78°C containing 4A molecular sieves (15-20 mg/L). After 3 h at -78°C, 1N NaOH was added, followed by extraction and chromatography to afford 208 mg of 3 (90%), anti syn 99 1. 

A valuable asymmetric route to homoallylic alcohols exploits the remarkably versatile chemistry of boranes.t ] The (Z)- and E)-crotylboranes (37) and (38) are prepared by reaction of the corresponding (Z)- and )- crotyl potassiums with (+)- or (-)-methoxydiisopino-campheylborane (36), (also known as IpC2BOMe),... 

Recovery of the wopropyl alcohol. It is not usually economical to recover the isopropyl alcohol because of its lo v cost. However, if the alcohol is to be recovered, great care must be exercised particularly if it has been allowed to stand for several days peroxides are readily formed in the impure acetone - isopropyl alcohol mixtures. Test first for peroxides by adding 0-6 ml. of the isopropyl alcohol to 1 ml. of 10 per cent, potassium iodide solution acidified with 0-6 ml. of dilute (1 5) hydrochloric acid and mixed with a few drops of starch solution if a blue (or blue-black) coloration appears in one minute, the test is positive. One convenient method of removing the peroxides is to reflux each one litre of recovered isopropyl alcohol with 10-15 g. of solid stannous chloride for half an hour. Test for peroxides with a portion of the cooled solution if iodine is liberated, add further 5 g. portions of stannous chloride followed by refluxing for half-hour periods until the test is negative. Then add about 200 g. of quicklime, reflux for 4 hours, and distil (Fig. II, 47, 2) discard the first portion of the distillate until the test for acetone is negative (Crotyl Alcohol, Note 1). Peroxides generally redevelop in tliis purified isopropyl alcohol in several days. 

Further investigation of allylpotassium complexes have shown that 2-isopropylallyl potassium does not show diastereotopism of the methyl groups at temperatures as low as —155 °C54,59. Therefore, the activation barrier for interconversion is on the order of 4 kcal mol 1 or lower. Both crotyl (19) and prenyl (20) potassium complexes are further examples of the preference for allylpotassium compounds to exist as symmetric it species. The potassium has the appropriate atomic radius to reach both C(i) and C(3). No increase in stabilization is gained upon addition of solvent. Allylcesium behaves in the same manner. In general, the theoretically calculated rotational barriers (Table 9) are higher... 

It is a colorless liquid with an oily-fruity odor with floral, petal-like notes. For synthesis, 1,3-cyclohexanedione is reacted with crotyl bromide in the presence of potassium hydroxyde to give the 2-alkenyl-substituted 1,3-diketone. Ring cleavage with sodium hydroxyde leads to the unsaturated keto acid which is reduced with NaBH4 under formation of the title compound [201]. 

Andreev and co-workers have undertaken extensive studies on the reactions of allyl, crotyl, and propargyl alcohols with 2-substituted pentafluoropropenes 14.11 Allyl and crotyl alcohol react at 5-20 C with various 2-substituted pentafluoropropenes 14 in the presence of potassium fluoride in dimethylformamide to give -substituted a-(trifluoromethyl) esters 16. Saponification yields the corresponding acids. 

The residue is cooled to 40° and slowly hydrolyzed (cooling as necessary) with 900 cc. of cold 6 N sulfuric acid, prepared from 145 cc. of concentrated sulfuric acid and 700 cc. of water. The oily layer is separated, washed once with water, and distilled at 60-70° while the pressure is lowered slowly from about 275 mm. to 65 mm. Finally the distillation is continued to 100° and 20 mm. This procedure permits separation of all the crotyl alcohol from the higher-boiling polymerization products. The aqueous layers are combined and distilled until the distillate no longer gives a test for unsaturation with a dilute solution of bromine in carbon tetrachloride. The distillate is then saturated with potassium carbonate, and the oily layer which separates is added to the product obtained by distillation of the oil. 

After drying over 10 g. of anhydrous potassium carbonate, the oil is decanted and fractionated through an 80-cm. Vigreux column at atmospheric pressure. Crotyl alcohol distils at 117-122°/760 mm., weight 130 g. (60%). This material is 93% pure as determined by titration with bromine in carbon tetrachloride. If the crude crotyl alcohol is dried for several days before distillation the product is 97% pure. Refractionation through a 110-cm. bead column gives material boiling at 121.2°/760 mm. which is 99.1 to 99.7% pure. 

Anionic Claisen rearrangement. Acceleration of the Claisen rearrangement of allyl vinyl ethers was originally observed with potassium hydride in HMPT, but even milder conditions are possible using sodium or lithium dimsylate. The catalyzed rearrangement is as stereoselective as the thermal counterpart. Thus vicinal asymmetric centers are formed selectively on rearrangement of (E)- and (Z)-crotyl ethers (equations I and II). 

The formation of olefinic nitriles from allylic halides is best accomplished with dry, powdered cuprous cyanide rather than with alcoholic alkali cyanides, with which side reactions such as isomerization and alcoholysis of the double bond are particularly bothersome. With cuprous cyanide the yields in the synthesis of allyl cyanide and methal-lyl cyanide are 84% and 86%, respectively. Higher allylic halides are subject to allylic rearrangements thus cuprous cyanide acts on crotyl halide (CH,CH CHCHjX) and methylvinylcarbinyl halide (CH,CHXCH = CH,) to produce the same mixture of isomeric nitriles (9 1) regardless of which halide is treated. Numerous cyanides of the allylic type (Cj-Ci4) have been prepared, although the possibility of an isomerization has not been considered. A similar isomerization has been observed in the reaction of sorbyl chloride and potassium cyanide. ... 

Allylic chlorides, e.g., allyl, methallyl, and crotyl chlorides, are very reactive and are employed in the synthesis of unsaturaled ethers Besides the usual coupling of the sodium alcoholate and halide in alcohol solutions other conditions have been described, including reaction of the alcohol and unsaturated halide in the presence of potassium carbonate or sodium hydroxide in acetone or water. The combination of anhydrous potassium carbonate and acetone is widely used in the preparation of allyl aryl ethers the reaction is aided by the addition of finely powdered potassium iodide. ... 

Figure 4 Structures of allyl- and crotyl-magnesium, -lithium and -potassium reagents as determined by isotopic perturbation studies. The magnesium reagent (a) exists as a o-structure and the potassium (b) and lithium (c)...

---