Esters reagents with

Reaction of Grignard reagents with es ters (Section 14 10) Tertiary alcohols in which two of the substituents on the hy droxyl carbon are the same may be pre pared by the reaction of an ester with two equivalents of a Grignard reagent... 

Esters react with two equivalents of a Grignard reagent to produce terti ary alcohols Two of the groups bonded to the car bon that bears the hy droxyl group in the terti ary alcohol are derived from the Grignard re agent... 

Section 20 9 Esters react with Gngnard reagents and are reduced by lithium aluminum hydride (Table 20 4)... 

One widely used method of formation of protected compounds involves polymer-supported reagents, with the advantage of simple workup by filtration and automated syntheses, especially of polypeptides. Polymer-supported reagents are used to protect a terminal — COOH group as a polymer-bound ester (RCOOR —( ) during peptide syntheses, to protect primary alcohols as... 

Trapping of the same Homer-Emmons reagent with an acid chloride leads to the formation of the a-fluaro- -keto esters in good yields [74] (equation 63) (Table 24)... 

Ttansmetalation of tliioetliets to organocopper compounds can also be performed in some special cases. Tluis, tteatment of the ester 119 with MeyCuLi-LiCN provides the copper reagent 120, which can be treated successfully witli several electrophiles such as allyl bromide ot acid chlorides to afford the expected products such as 121 iScbeme 2.54) [115, 116]. 

By reaction of an a-halo ester 1 with zinc metal in an inert solvent such as diethyl ether, tetrahydrofuran or dioxane, an organozinc compound 2 is formed (a Grignard reagent-like species). Some of these organozinc compounds are quite stable even a structure elucidation by x-ray analysis is possible in certain cases ... 

An interesting appetite suppressant very distantly related to hexahydroamphetamines is somanta-dine (24). The reported synthesis starts with conversion of 1-adamantanecarboxylic acid (20) via the usual steps to the ester, reduction to the alcohol, transformation to the bromide (21), conversion of the latter to a Grignard reagent with magnesium metal, and transformation to tertiary alcohol 22 by reaction with acetone. Displacement to the fomiamide (23) and hydrolysis to the tertiary amine (24) completes the preparation of somantadine [6]. 

This is followed by hydrolysi.s of the ester moieties with potassium carbonate and reesterification of the carboxy moiety with diazomethane to produce intermediate 65. The solitary free alcoholic hydroxyl at C-9 is oxidized with Collins reagent and the silyl ether groups are removed with acetic acid to give enprostil (63) [15]. 

Esters react with Grignard reagents to yield tertiary alcohols in which two of the substituents bonded to the hydroxyl-bearing carbon have come from the Grignard reagent, just as LiAlH4 reduction of an ester adds two hydrogens. 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

Racemic l-methyl-2-butenylboronates (E)- and (Z)-3 may be prepared selectively via reactions of the l-methyl-2-butenyl Grignard reagent with the appropriate borate ester. Use of triisopropyl borate provides a 96 4 mixture of (E)-3l(Z)-3 on a 0.36 mol scale15. Use of a bulkier borylating agent, such as 2-isopropyloxy-4,4,5,5-tetramethyl-l,3,2-dioxaborolane, reverses the selectivity, enabling a 91 9 mixture of (Z)-3/( )-3 to be obtained on a 0.5 mol scale. The diastereomeric purity of this mixture may be enhanced to 95 5 by treatment with 0.15 equivalents of benzaldehyde, since ( )-l-mcthyl-2-butenylboronatc ( )-3 is more reactive than (Z)-3. Repetition of this process provides (Z)-3 that is 98% isomerically pure. 

---