Alkenyl alcohols

This procedure illustrates a general method for the stereoselective synthesis of ( P)-disubstitnted alkenyl alcohols. The reductive elimination of cyclic /3-halo-ethers with metals was first introduced by Paul3 and one example, the conversion of tetrahydrofurfuryl chloride [2-(chloromethyl)tetrahydrofuran] to 4-penten-l-ol, is described in an earlier volume of this series.4 In 1947 Paul and Riobe5 prepared 4-nonen-l-ol by this method, and the general method has subsequently been applied to obtain alkenyl alcohols with other substitution patterns.2,6-8 (I )-4-Hexen-l-ol has been prepared by this method9 and in lower yield by an analogous reaction with 3-bromo-2-methyltetra-hydropyran.10... 

Alkenyl alcohols, (E) disubstituted, 55, 66 ALKYL HALIDES, alkenes from, 55, 103 C-ALKYLATION, phase transfer catalysis... 

Halo-ethers can be formed by the reaction of alkenyl alcohols with various reagents. Hept-6-en-l-ol reacts with (collidine)2l PFg, for example, to form 2-iodomethyl-1 -oxacycloheptane. ... 

Treatment of phenylchalkogen substituted alkenyl alcohols with /-BuOK provided useful tetrahydrofurans stereoselectively <96JOC8200>. A concise synthesis of cis- and trans-theaspirones via oxonium ion-initiated pinacol ring expansion was developed <96JOCl 119>. 

C8-C22 alkyl and alkenyl alcohols Alkyl acids and esters (16) Unidentified compounds possible terpenoid isomers and... 

Alkenes, chain elongation, 56, 32 Alkenyl alcohols, (E J-disubstituted, 55, 66 A -Alkenylhydroxylamines, 58, 108... 

The isoxazolidines (47) and (48) were obtained by cyclization of the corresponding ketone-derived exocyclic nitrones (Scheme 11).22 Such reactions have been used for natural product sysnthesis, as in the conversion of isoxazolidine (49) to ( )-hirsutene. Methylation and catalytic hydrogenolysis provided a y-dimethylamino alcohol, which underwent Cope elimination to provide an alkenyl alcohol in a key step. A related synthesis of ( )-7,12-sechoishwaran-12-ol is also reported. 

Alkenyl alcohols, into tj3-allyl palladium complexes, 8, 365 u-Alkenyl-aldehydes, in Ti-promoted Pauson-Khand reactions, 4, 270... 

Rhodium(ll)-catalyzed etherification of an allylic carbonate with enantiopure alkenyl alcohols 246 followed by RCM proceeds with excellent diastereoselectivity to afford syn-247 or /f-3,6-dihydropyrans 248 in high yield (Scheme 68) <2004AGE4788>. This methodology can be extended to the preparation of chiral 2,3,6-trisubstituted 3,6-dihydropyrans <2004JA8642>. 

Seven-membered lactones can also be prepared in good yields by ruthenium-catalysed cyclocarbonylation of alkenyl alcohols (e.g. 119 from 118) [01TL5459] or by ring closing metathesis using Grubbs imidazolidine catalyst (e.g. 121 from 120, n=2) [02H85]. 

In an earlier investigation by the author [1] an additional acyclic diene metathesis ruthenium polymerization catalyst, (I), was identified and used in the metathesis of alkenyl alcohols. 

Although thus far a number of reports have been made on mthenium complex-catalyzed isomerization of alkenyl alcohols to saturated aldehydes or ketones, the mechanistic details of these reactions have not yet been fully elucidated. It has been generally accepted that isomerization of the alkenyl alcohol forming a carbonyl compound proceeds via an intermediate enol. However, developments in mechanistic studies have advanced recently, and a new mechanism which involves an intermediary mthenium alkenylalkoxide is proposed by Trost et al. for isomerization of allylic alcohols catalyzed by CpRuCl(PPh3)2 (Cp = [1]. Gmbbs et al. also proposed... 

A novel type of isomerization of alkenyl alcohol, repositioning of the carbon-carbon double bond, is catalyzed by RuCl2(PPh3)3. In the presence of a catalytic amount... 

Huang, G, Holhngsworth, R I, The stereoselective conversion of 2-alkenyl alcohols to (R)- or (S)-atkane-l,2-diols using D-glucose as chiral auxihary. Tetrahedron Lett., 40, 581-584, 1999. 

The reaction is believed to proceed via a mechanism analogous to hydroamina-tion and hydrophosphination. There is experimental evidence for a rate-determining insertion step (Fig. 23). The high oxophilicity of the lanthanide ion results in a high barrier for the olefin insertion and therefore, diminished reactivity of alkenyl alcohols. Rare-earth metal triflates are also capable to catalyze cyclization of alkenyl alcohols in ionic liquids [193], although the mechanism is unlikely to be similar to the o-bond metathesis mechanism discussed above. 

Zhou et al. [18] reported the use of calcium in ethylenediamine for reductive cleavage of dihydropyrans (Scheme 4.6). In 5,6-dihydro-2H-pyrans 19, the allylic C-O bond is cleaved selectively to give a mixture of alkenyl alcohol 20 and saturated alcohol 21 in a 98 2 ratio with an overall yield of 58-60%. Application of the same reducing agent to 3,4-dihydro-2H-pyran (22), however, led to tetrahydro-pyranyl pentyl ether 23 in 51% yield. This involves reduction followed by an addition process. 

Lenoble et al. reported the cyclocarbonylation of the alkenyl alcohol 191 with carbon monoxide in the presence of palladium, phosphine, and tin catalysts gave the nine-membered lactone 192 selectively (Scheme 64).135c... 

Wittig reaction of aliphatic aldehydes and alkenyl alcohols with 50% NaOH or solid K2CO1. 

The pinacol-like rearrangement of halohydrins typically require elevated temperatures or extended reaction times. One notable exception is the low temperature rearrangement of vinyl alcohols 12. derived from the corresponding a-halo ketones by addition of a metalloalkyne and direct reduction of the resulting adduct with lithium aluminum hydride, providing an efficient and stereocontrolled access to a-alkenyl alcohols 1364-6 The intermediacy of vinyl alcohols 12, as a necessary precedent to rearrangement has been inferred from the observation that metal alkoxides 11 (M = Li, Mg) do not rearrange under the reaction conditions and are stable even at elevated temperatures. 

Sequential Rh-catalysed etherification of the allylic carbonate using the Cu(I) alkoxide derived from the enantiomers of the alkenyl alcohols followed by a RCM occur with excellent regio- and enantiospecificity and lead to cis- and traws-disubstituted dihydropyrans <04AG(E)4788>. 

Figure 2.15 Automated solid phase oligo-/polysaccharide synthesis. Glycosyl donor (A) is coupled to a solid phase Merrifield-like resin through an alkenyl alcohol linker. The double bond allows for clean removal of product at the end of solid phase synthesis by metathesis using Grubb s catalyst in the presence of ethylene gas. For protecting groups, see Fig 2.13. Trimethyl silyltriflate (TMSOTf) activates the glycosyl donor through controlled removal of the trichloroacetamidate.

The Sharpless asymmetric epoxidation (sec. 3.4.D.i) exploits this chelation effect because its selectivity arises from coordination of the allylic alcohol to a titanium complex in the presence of a chiral agent. The most effective additive was a tartaric acid ester (tartrate), and its presence led to high enantioselectivity in the epoxidation.23 An example is the conversion of allylic alcohol 40 to epoxy-alcohol 41, in Miyashita s synthesis of the Cg-Ci5 segment of (-t-)-discodermolide.24 in this reaction, the tartrate, the alkenyl alcohol, and the peroxide bind to titanium and provide facial selectivity for the transfer of oxygen from the peroxide to the alkene. Binding of the allylic alcohol to the metal is important for delivery of the electrophilic oxygen and... 

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