4-Pentenol

The Pd—C cr-bond can be prepared from simple, unoxidized alkenes and aromatic compounds by the reaction of Pd(II) compounds. The following are typical examples. The first step of the reaction of a simple alkene with Pd(ll) and a nucleophile X or Y to form 19 is called palladation. Depending on the nucleophile, it is called oxypalladation, aminopalladation, carbopalladation, etc. The subsequent elimination of b-hydrogen produces the nucleophilic substitution product 20. The displacement of Pd with another nucleophile (X) affords the nucleophilic addition product 21 (see Chapter 3, Section 2). As an example, the oxypalladation of 4-pentenol with PdXi to afford furan 22 or 23 is shown. 

Remarkably, 1,3-dienes have been shown to serve as homoallyl anion equivalents and react with aldehydes in the presence of a catalytic amount of Ni(acac)2 and a stoichiometric amount of triethylborane to provide bis-homoallyl alcohols, 4-pentenols 40, exclusively (Eq. 11) [27,28]. 

The homoallylation is applicable to multigram-scale experiments (Scheme 15) [36]. In the presence of 3mol% of Ni(acac)2, a mixture of 25 mmol of benzaldehyde, 50 mmol of Et3B, and 50 mmol of isoprene provides anti-3-methyl-l-phenyl-4-pentenol in 92% yield (4.1 g) with excellent 1,3-anti stereoselectivity. The product is purified by means of a single Kugelrohr distillation of the reaction mixture after an appropriate aqueous workup. 

The 14C labelled 4-pentenals, 233, have been converted to their dimedone derivatives for radio assay. The lsO-233 has been reduced to 4-pentenol for MS isotopic assay. The average lsO and 14C KIEs in the rearrangement of 232 were found to be ... 

Both diorganotellurium(IV) and diorganoselenium(IV) dibromides are known, stable compounds, which permits a direct comparison of the selenium(IV) and tellurium(IV) compounds. Di-4-chlorophenyltellurium(IV) dibromide (36) and one equivalent of pyridine were essentially unreactive with respect to bromination of either 4-pentenoic acid or 4-pentenol. With either substrate, 36 gives only 2-3% conversion to brominated products after several days of reaction (Fig. 17). In contrast, diphenylselenium(IV) dibromide (1, Fig. 1) and 2-(dimethylaminomethyl)-phenyl phenyl bromoselenonium bromide (37) gave essentially complete bromination of either 4-pentenoic acid or 4-pentenol in 1 h in the presence of one equivalent of pyridine as shown in Fig. 17. 

We have studied the anodic oxidation of unsaturated alcohols using the controlled potential electrolysis (E = 1.9V vs SCE) in CH3CN-O.I mol/1 Et4NC104 solution in a divided cell [110]. The oxidation of 4-pentenol after consumption of 0.8 F/mol gave 2-methyltetrahydrofuran and tetrahydropyran as the major products. The oxidation of 5-pentenol gave 2-methyltetrahydro-pyran and oxepam, while the oxidation of 3-butenol under the same reaction conditions did not give the cyclic products. We rationalized this reaction as the electrongenerated acid (EGA) catalyzed intramolecular cyclization (Scheme 44). 

Diaryltellurium diiodides afford the iodocyclization of 4-pentenol. Diaryltellurium dibromides give only traces of bromotetrahydrofurans with 3-butenol and 4-pentenol. ... 

Typical procedure7 A solution of 4-pentenol (0.0860 g, 1.00 mmol), bis(p-chlorophenyl) tellurium diiodide (0.605 g, 1.00 mmol), and pyridine (0.080 g, 1.00 mmol) was heated at reflux in 10 mL of chloroform for 4 days. The reaction mixture was concentrated in vacuo, and the residue was purified via chromatography on silica gel eluted with 1 1 hexane/ethyl acetate to give 0.121 g (57%) of the iodotetrahydrofuran and 0.30 g (85%) of the diaryl-telluride. 

Ethyi-4-pentenol (5, R = CH2CH = CH2 RJ = C2H5) Typical Hydride Reduction Procedure22 ... 

For systems in which 6-endo cyclization is favored only by alkyl substitution, the ratio of 5-exo to 6-endo cyclization appears to be sensitive to both reaction conditions and substrate structure. Cyclizations of a variety of 5,5-dimethyl-4-pentenols (equation 34) are shown in Table 8. Although the use of 2,4,4,6-... 

Pentenyloxymethyl chloride, CH,==CH(CH2)3OCH2Cl (POMC1), 1. The reagent is prepared by reaction of 4-pentenol with formaldehyde and hydrogen chloride. 

Keto aldehydes are prepared by the allylation of aldehydes. Reaction of 2-p-tolylpropanal (27) with allyl bromide gave 2-p-tolyl-2-methyl-4-pentenol (28) in 63% yield. The oxidation of the terminal... 

The stereoselective preparation of rfl .v-2-hydroxymethyl-5-subslituted tetrahydrofurans from 4-pentenols is possible by oxidative cyclization catalyzed by cobalt(ll) salts. Both cobalt(II) trifluoroacetate and cobalt acetylacetonate have been employed for the cyclization, but better yields are obtained with Co(modp)2 (l)45. 

Similar results were obtained from cyclic amidals, e.g., 14, derived from salicylamide and 4-pentenol. Rapid cyclization occurred on treatment of 14 with a 50 50 mixture of mercury(ll) acetate and mercury(ll) trifluoroacetate, to give a diastereomeric mixture of 15 in 90% yield, in which the 1,3-tram-isomer predominates 65. 

Reminiscent of the succinate formation are intramolecular dialkoxycarbonyla-tions [33], e.g., of 3-butenols [34], and 4-pentenols [35] leading to the corresponding lactones. 

The above intermolecular processes, while interesting and instructive, are of relatively limited scope because the high concentration of nucleophiles required limits them to readily available, volatile alcohols. Intramolecular processes therefore hold more promise. In an early ESR study of the interaction of hydroxyl radicals with 4-pentenol, Davies and Gilbert observed the predominant formation of the 2-tetrahydrofuranylmethyl radical. It was thought that this chemistry could best be attributed to cyclization of the alcohol onto the alkene radical cation, but the possibility of the hydroxyl radical adding to the alkene to give a 1,5-dihydroxy-... 

Pentenols. Alkenes undergo allylboration with allyldibromoborane. Oxidation of the adducts gives 2-substituted 4-pentenols. 

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