Peterson alkene synthesis

In the Peterson s synthesis the b-hydroxysilanes are converted to alkenes in either acidic or basic solution. 

Which of the following methods of alkene synthesis appear reasonable a) Witrig b) Homer-WtkIsworth-Emmons or c) Peterson olefination ... 

Mechanism The Peterson alkenation offers the synthesis of desired alkene stereoisomer by careful separation of the two diastereomeric intermediate P-hydroxysilanes and subsequently performing elimination under two different conditions. 

Synthesis and Reaction Chemistry of a,p-Unsaturated Acyl Complexes Derived from (2). Two methods for the preparation of optically active ( )- and (Z)-a,p-unsaturated iron acyls from (2) have been reported." One method involves aldol condensation of (2) with aldehydes followed by 0-methylation to produce diastereomeric acyls (18). This mixture (18) is then treated with Sodium Hydride to produce predominantly ( )-a,p-unsaturated acyl complexes (19) (eq 13). Alternatively, (2) can be depro-tonated and treated with Chlorotrimethylsilane to produce the C-silylated complex which is subsequently deprotonated and treated with an aldehyde. This Peterson alkenation produced mixtures... 

In the case of base-induced elimination, the Peterson alkenation relies on the strong bond formed between silicon and oxygen, and the ready propensity for silicon to be attacked by alkoxide, to drive the reaction. In the original study by Peterson, the -silylcarbinols were prepared by the addition of (trimethylsilyl)methylmagnesium chloride to the carbonyl. The caibinols were subsequently eliminated by treatment with sodium or potassium hydride or with sulfuric acid to form the methylene derivatives in excellent yield. The Peterson reaction has proven to be of general utility in the synthesis of alkenes. ... 

In analogy to the Peterson alkenation, the intermediate hydroxyphosphine oxidn (269) cm be prepared by addition to epoxide derivatives (268 Scheme 36). Overall yields are high for this process, and this sequence can be applied to the synthesis of phosphonate intermediates as well. Warren has studied hydroxy-directed epoxidation. Provided the allylic phosphine oxide is trisubstituted, as is (270) in equation (6S), these oxidations proceed with good selectivity. Ring opening can then be undertaken to generate the hyth-oxyphosphine oxide. 

Boeckman and coworkers studied the reaction of bis(thmethylsilyl) ester (361) with aldehydes to form the silyl-substituted unsaturated ester (362 equation 86). The anion was formed with potassium or lithium diisopropylamide. Other metals, such as magnesium or aluminum, were introduce by treating the lithium anion with Lewis acids. The addition step produced a single diastereomer, en ling the effects of counterion and steric bulk on the elimination to be ascertained. Excellent selectivity for the ( )-isomer (362) may be obtained by using K or Li cations and a sterically hindered aldehyde. In studies directed toward the synthesis of substituted pseudomonic acid esters, the Peterson alkenation was utilized to form a mixture of (Z)- and ( )-alkene isomers, one example of which (365) is depicted in equation (87). In this example the conditions were optimized to form the highest degree of selectivity for the (Z)-alkene. 

The use of cerium trichloride for the Peterson alkenation has been q)plied by Ueda and cowoikers for nucleoside synthesis (Scheme S2). The anion was generated with LDA/cerium trichloride and condensed with the aldehyde (375). The product was treated with KH in THF and the pyrimidopyridine (377) isolated in S0% yield. 

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