Iodohydrin esters

The conditions necessary for rearrangement of 2/3,3a-(diaxial) iodohydrin esters [e.g. (28)] to the transposed diequatorial isomers [e.g. (29)] have been further... 

Elimination. The highly stereoselective conversion of iodohydrin esters to alkenes [erythro ( ), threo — (Z)] by the allyltrimethylsilane-TiCl mixture enables stereoretentive deoxygenation of epoxides via the iodohydrins. 

Magnesium iodide reacts with a,p-epoxy esters to form p-iodo-a-hydroxy esters selectively (200 1). The regioselectivity is attributed to favorable chelation of the iodohydrin. These products are reduced by Bu,SnH to hydroxy esters in 75-95% overall yields with retention of the original configuration at the a-position. 

Analysis of Reagent Purity enantiomeric purity can be assessed by the following procedures. Procedure A (no deriva-tization) Chiral HPLC on a Diacel OD column (10 pim, 0.46 X 25 cm) flow, 0.7 mL min" 99 1 hexane-2-propanol Ir (5) enantiomer, 51.2 min (R) enantiomer, 53.9 nrin. Procedure B the reagent is opened to the iodohydrin the crude iodohydrin is esterified with (R)-(+)-a-methoxy-a-(trifluoromethyl)phenylacetyl (MTPA) chloride the resulting crude MTPA ester is analyzed by chiral HPLC and H NMR. ... 

The release of ring strain in epoxides is probably responsible for the high reactivity of these special ethers. HI opens epoxides under mild conditions stereospecifically to iodohydrins (Scheme 26). The mechanism is similar to the reaction of bromide with epoxides (see Section 1.7.3.3). It should be noted, however, that reduction of epoxides to alkenes may occur if vicinal diiodides are intermediately formed, which can lose I2 under the reaction conditions. With the combination of acyl chloride and Nal unstable diiodides are avoided and 2-iodoethyl esters are formed from oxiranes (Scheme 27). ° ... 

The generation of an alkene by the reaction of a v/c-disulfonate ester with iodide (the Tipson-Cohen reaction) has been known since 1943 and in some cases it has proved useful where other methods have failed, as in the preparation of the spirocyclic triene (54 Scheme 22). The mechanism probably involves an initial nucleophilic displacement to give an iodohydrin sulfonate, which then undergoes iodide-induced elimination to the alkene. Methanesulfonates can be used as well as arenesulfonates. 

Further proof of the intermediacy of the iodohydrins 85 in the formation of the hydroxy-tetrahydrofurans 80 came from two sources. Firstly, treatment with potassium carbonate led to formation of the corresponding epoxides. Secondly, by providing a second alkene function, suitably positioned to trap the iodohydrin hydroxyl by a 6-eto-trig iodocyclization, we have been able to intercept these species and hence define a new approach to substituted pyrans. Thus, treatment of the dienyl hydroxy-ester 90 with iodine and NaHCO, resulted in the formation of pyrans 92 in the ratio of 3.2 1. Presumably, initial iodohydrin formation 91 is followed by a relatively non-stereoselective 6-exo cyclization. Further chemistry of such products has yet to be carried out, especially efforts to distinguish the two iodine atoms and to cyclize to give furopyran systems <01M1001>. 

One simple procedure allows the synthesis of phosphatidylserine by condensation of phosphatidic acid with an amino- and carboxy-protected serine. iV-Carbobenzoxyl-DL-serine benzyl ester was condensed with the phosphatidic acid in the presence of tri-isopropylbenzenesulphonyl chloride. The protecting groups were then removed by hydrogenation which limits the method to saturated phosphatidylserines. However, the use of different protecting groups should allow this method to be used for unsaturated compounds. An alternative procedure involves the introduction of the phosphate and serine functions via a complex silver salt to glycerol iodohydrin diesters (de Haas etal, 1964). 

Cl8HigOg, 2,7-Dihydroxy-5-methyl-[3,4-d](2, 3 -dihydro-2, 3, 3 -tri-methylfurano)naphthalic-1,8-anhydride, 46B, 597 Ci8Hi7Br03, Thujic acid p-bromophenacyl ester, 31B, 262 ClbHi8N2O7S2, Epicorazine A monohydrate, 43B, 769 CibHibOb, Samaderine A, 44B, 546 C18H18O7, Senepoxide, 42B, 472 CisHiglOg, Crotepoxide iodohydrin, 34B, 341... 

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