Homoenolate anion equivalent

Richardson, S. K. Jeganathan, A. Watt, D. S. l-Vinyl-4-methyl-2,6,7-trioxabicyclo[2.2.2]oc-tanes unsaturated homoenolate anion equivalents. Tetrahedron Lett. 1987, 28, 2335-2338. 

The title transformation provides an alternative pathway for the construction of the cyclopropane ring from a synthon of three carbons. The intramolecular cyclization of homoenolate anion equivalents is represented in Scheme 11, Eq. (ii). In practice, several routes involving metals such as Mg, Zn, and Ti, as well as different homoenolate precursors, have been developed [17a-e]. 

Siloxycyclopropanes are known as homoenolate anion equivalents and have been favorably utilized in organic synthesis. Murai, Sonoda, and coworkers found that desi-lylative dimerization of the siloxycyclopropanes occurs on exposure to AgBp4 [26a], The reaction of 54 gives 1,6-diketone 55 in good yield (Sch. 13). The 8-silver ketone 56 is considered to be a key intermediate in the dimerization. The intermediary ver ketone, generated from siloxycyclopropane 57 and AgP, can be successfully trapped with allyl chloride to afford a (5,e-unsaturated ketone 58 [26b]. 

Heteroatom-substituted allylic anions as homoenolate anion equivalents 862... 

In accordance with this model one finds diastereoselectively anti products on reaction of aldehydes with ( )-allyl compounds, whereas allyl systems with the (Z)-configuration give mainly syn products and it is even possible to effect asymmetric induction. As the double bond of the product can be oxidatively cleaved to a CW3 group, the reaction can be regarded as a stereoselective aldol reaction, an aspect which explains the widespread interest in this type of reaction. With heterosubstituted allylic anions it is sometimes possible to effect predominantly y-attack with different electrophiles by the choice of the heteroatom.2 For instance it is well known that with sulfur substituents like —SR, —SOR or —SOjR the a-attack dominates, but doubly lithiated allenethiol possesses high y-reactivity and can be used as a homoenolate anion equivalent in reaction with electrophiles such as alkyl halides (Scheme 7). ... 

On the other hand the inherent a-selectivity of allylsulfur carbanions can sometimes be transformed to a y-reactivity by a sigmatropic rearrangement, earning in addition the stereoselectivity typical for such reactions (see Section 4.S.2.3). Due to their significance in synthesis a lot of work has been done on reactions of heteroatom-substituted allyl anions with special emphasis on their use as homoenolate anion equivalents. The more recent developments, with the possibility of introducing diastereoselectivity, will be discussed later in Section 4.S.3.2.I. 

There are two main synthetic applications where the reaction of an allyl system with electrophiles is accompanied by an allylic rearrangement. One consists of the use of heteroatom-substituted allylic anions as homoenolate anion equivalents and the other represents a synthetically valuable alternative to the aldol reaction by addition of allyl metal compounds to aldehydes. 

Heteroatom-substituted allylic anions can serve as homoenolate anion equivalents in reaction with electrophiles, when y-attack can be realized and the formed vinyl heterocompound can be hydrolyzed to an aldehyde (Scheme 76). ... 

Several other chiral homoenolate anion equivalents have been successfully exploited for asymmetric homoaldoi reactions, e.g. (48) and (49), ° but their preparation seems more laborious than that of the carbamates (47). 

Warren and coworkers have described the alkylation of (diphenylphosphinoyl)alkyllithiums with epoxides as an effective means of synthesizing 3-(diphenylphosphinoyl) ketones, homoenolate anion equivalents. The treatment of the adducts of lithiated phosphine oxides and epoxides with base to form cyclopropanes was reported by Toscano et al ... 

Heteroatom-substituted allylic anions as homoenolate anion equivalents 4.5.322 Addition of ally Imetal compounds to aldehydes synthesis of homoallylic alcohols... 

General Synthesis.—/3-Substituted esters can be prepared from a,/3-unsaturated aldehydes by alkylations of the homoenolate anion equivalents (83), formed from the aldehydes by [1, 2] addition of diethyl trimethylsilylphosphite or the corresponding phosphorodiamidate [Et3SiOP(NMc2)2], followed by metallation with lithium di-isopropylamide (Scheme 32). Overall yields are often in the region of 60—80%. 

Homoenolate Anion Equivalent. The reaction of (1) with acid chlorides in the presence of titanium(IV) chloride affords the corresponding y-keto aldehydes after hydrolysis (eq 2) O-Acylation to form the 1-silyl allyl ester (17-30%) competes with the Se alkylation of the double bond. Bulkier silyloxy derivatives give y-keto aldehydes in higher yield. 

The species (24) is a chiral homoenolate anion equivalent, and reacts with alkyl halides to give chiral j8-substituted aldehydes after hydrolysis. The anion (25) can also act as a homoenolate anion equivalent or, alternatively, as an acyl anion equivalent. For instance, reaction at -78 C results in electrophilic attack at the a-position (acylanion equivalent), whereas at 0°C y-attack is observed (homoenolate anion equivalent). 

Discuss (in general terms) how the anion derived from 149 served as a homoenolate anion equivalent. (Juvabione-20)... 

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