Unsaturated Alcohols—Alkenols

The simplest unsaturated alcohol, ethenol (vinyl alcohol), is unstable with respect to ethanal and has never been isolated (see Sections 10-5A and 13-5B)  

Other simple alkenois (enols) also rearrange to carbonyl compounds. However, ether and ester derivatives of enols are known and can be prepared by 

The enol of 2-oxopropanoic acid (pyruvic acid) is of special biological interest because the phosphate ester of this compound is, like ATP (Section 15-5F), a reservoir of chemical energy that can be utilized by coupling its hydrolysis (AG° = —13 kcal) to thermodynamically less favorable reactions  

In fact, the ester can be utilized to synthesize ATP from ADP that is, it is a phosphorylating agent, and a more powerful one than ATP  

Enols usually are unstable and are considerably more acidic than saturated alcohols. This means that the conjugate bases of the enols (the enolate anions) are more stable relative to the enols themselves than are alkoxide ions relative 

---

Both Z- and E-configurations of carbon-carbon double bond are an important structural moiety of insect pheromones. The synthesis of unsaturated alcohols has attracted considerable attention of organic chemists in recent years because such alcohols and their acetates are known to be insect sex attractants. Recently, a very convenient, general, one pot synthesis of Z alkenols132) and Z-alkenols 133) via organoboranes has been reported. 

Substituted olefins also complex with CuCl. The halide dissolves in allyl alcohol owing to complex formation 183, 184). Other unsaturated alcohols give complexes of the type (alkenol)CuCl and [(alkenol)Cu] + when added to solutions of CuCl in aqueous HCl 185). Similar complexes are formed with various unsaturated carboxylic acids, and the stability of the complexes is influenced by the stereochemistry about the double bond 13). Maleic acid, however, forms the anionic complex [CuCl(02C -CH=CH.C02H)] in addition to the neutral and cationic complexes 11, 12). 

Type III Reactions and Other Reactions of Acetals. Treatment of symmetric acetals with alkenols or al-kynols in the presence of TiCU results in transacetalization to give mixed acetals such as (285) which react further via cation (286) to give cyclic products such as (287) in 50-99% yield. In this one-pot procedure the alkenic acetal need not be isolated. Acetoxyalkoxyacetic esters, such as (288), prepared in two steps from methyl glyoxylate and unsaturated alcohols, cyclize under the influence of SnCU in CH2CI2 to give oxacyclic carboxylic esters such as (290). These reactions proceed through the intermediacy of methoxycarbonylcarbonium ion (289). 

Grmstone, F.D., andR. P. IngUs, Ox fmercuration-Demercuration of Unsaturated Alcohols. A New Procedure for the Identification, Isolation, and Estimation of A3t, A4, and A5 Alkenols, Chem. Phys. Lipids 10 105-113 (1973). 

The oxidation of benzylic type alcohols and alkenols with the double bond more than three carbon atoms distant from the hydroxyl group leads to unsaturated carboxylic... 

---