Allylic phosphonates lithiated

Alkenyl-3-phosphoryl chromanones and their thio- derivatives (217) have been synthesized from lithiated allyl phosphonates (218) and salicylate. It is... 

For lithiated allylic phosphonates, the nature of the carbon substituent affects the regioselectivity of the initial silylation as well as the reactivity of the resulting silylated anion.Whereas diethyl... 

Allyl anions (38a),(38b) and (38c) exhibit a similar regioselectivity toward electrophiles, and thus serve as homoenolate synthons. Addition of titanium tetraisopropoxide to (39) followed by condensation with aldehydes gives the anti adducts exclusively, which can be converted to the (Z)-1,3-dienes upon treatment with methyl iodide (Scheme 18). The ( -1,3-dienes can be prepared from the lithiated allyldiphenylphosphine oxide. The stabilized allylic phosphonate anion (40) condenses with carbonyl... 

In contrast to allylic phosphine oxides, phosphonates, sulfones and sulfoxides, the chemistry of lithiated allylic sulfoximines has been less extensively developed25 27. The reaction of lithiated racemic A-phenyl-A -(4-rnethylphenyl)-S -(2-propenyl)sulfoximine with either 2-cy-clopentenone or 2-cyclohexenone gave a complicated mixture with 1,4-oc-ad ducts being slightly favored over the 1,4-7-adducts. The yields of these adducts were poor25. In contrast, lithiated racemic Ar-tert-butyldiphenylsilyl-5-phenyl-5,-(2-propenyl)sulfoximine gives mainly 1,4-y-ad-ducts on reaction with the same enones26. 

Previous syntheses of terminal alkynes from aldehydes employed Wittig methodology with phosphonium ylides and phosphonates. 6 7 The DuPont procedure circumvents the use of phosphorus compounds by using lithiated dichloromethane as the source of the terminal carbon. The intermediate lithioalkyne 4 can be quenched with water to provide the terminal alkyne or with various electrophiles, as in the present case, to yield propargylic alcohols, alkynylsilanes, or internal alkynes. Enantioenriched terminal alkynylcarbinols can also be prepared from allylic alcohols by Sharpless epoxidation and subsequent basic elimination of the derived chloro- or bromomethyl epoxide (eq 5). A related method entails Sharpless asymmetric dihydroxylation of an allylic chloride and base treatment of the acetonide derivative.8 In these approaches the product and starting material contain the same number of carbons. 

The most popular method for generation of a-thio-carbanion (migration terminus) is direct lithiation (deprotonation) with alkyllithium or lithium amide. These deprotonation methods are widely applicable to various substrates, not only benzyl or allyl sulfides , but also dithioacetals 142 which form 143 (equation 83), and a phosphonate substituted system 144 which gives 145 (equation 84). ... 

The 1,4-addition reaction of stabilized allylic carbanions with conjugated enones is normally complicated by the ambident reactivity of the carbanion. Clean 7-selective conjugate addition to cyclic enones, however, has been observed with lithiated allylic sulfoxides, phosphine oxides and phosphonates... 

Lithiated ( )- and (Z)-2-alkenylphosphine oxides and phosphonates react with cyclic enones in a 1,4-conjugate addition manner (Schemes 19 and 20). The ( )- and (Z)-allylic anions react in highly dia-stereoselective fashion to deliver respectively syn and anti vinylic phosphine oxides and phosphonates. Chiral allylphosphonyl anions undergo enantioselective 1,4-addition with cyclic enones of varying... 

Reactions of lithiated ethyl 6-(dimethoxyphosphoryl)cyclohex-l-enecarboxylate with aliphatic, aromatic, and unsaturated aldehydes have been studied and determined to proceed with a or 5 regioselectivity. Such an unusual regioselectivity resulted from the contribution of two allylic carbanions one, stabilized by the phosphonate moiety and the other stabilized by the carboethoxy group. The course of the reaction depends mainly on the stmcture of the aldehyde and the reaction conditions. The products of Horner-Wadsworth-Emmons reaction were formed under kinetic conditions, whereas the 5-adducts were obtained as thermodynamic products. 

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