Tetrahydrofurans 1-iodo

A versatile method for the direct C-21 halogenation of a 20-ketopregnane was discovered by Ringold and Stork it consists of reaction with iodine-calcium oxide in tetrahydrofuran-methanol, and the resulting 21-iodo compound is displaced by acetate in the usual fashion ... 

The primary product of hypohalite photolysis is a 1,5-halohydrin, the stability of which increases on passing from iodo- to bromo- to chloro-hydrins. If spontaneous elimination of hydrogen halide does not occur, the halohydrins can be converted into tetrahydrofurans by base treatment. In several instances it has been possible to isolate the intermediate... 

B. 2-(4-Methoxyphenyl)-2-cyclohexen-1-one. A 500-mL, round-bottomed flask, equipped with a 1.5-in. Teflon-coated magnetic stirring bar and an argon inlet adaptor, is charged with 10.02 g (45.1 mmol) of 2-iodo-2-cyclohexen-1-one, 10.69 g (70.4 mmol, 1.56 eq) of 4-methoxyphenylboronic acid (Note 8), 16.72 g (72.1 mmol, 1.6 eq) of silver(l) oxide (Ag20) (Note 9), 0.85 g (2.8 mmol, 6 mol %) of triphenylarsine (Note 10), 0.53 g (1.4 mmol, 3 mol %) of palladium(ll) bis(benzonitrile)dichloride (Note 11), 200 mL of tetrahydrofuran (THF) and 25 mL of water (Note 12). The reaction mixture, flushed with argon, is stirred for 1 hr and then quenched by the addition of 125 mL of saturated aqueous ammonium chloride. After the solution is stirred for 1 hr, the... 

Isosorbide and isomannide are important by-products of the starch industry, arising from dehydration of D-sorbitol and D-mannitol. These commercial starting materials provide an easy and inexpensive access to optically pure functionalized tetrahydrofurans like 04,05-isopropylidene-1-iodo-3,6-anhydro-1-deoxy-D-glucitol and 04,05-isopropylidene-l-iodo-3,6-anhydro-1-deoxy-Q-mannitol. This procedure describes a preparation of the former compound and the epoxide derived therefrom. 

To the submitters knowledge, 04,05-isopropylidene-1-iodo-3,6-anhydro-1-deoxy-D-glucitol and 04,05-isopropylidene-1,2 3,6-dianhydro-D-glucitol have not been prepared before. However, the corresponding isomannide derivatives have been obtained in five steps from mannitol in low overall yield by Foster and Overend in 1951.6 7 The present method is a simple, rapid and inexpensive route to multigram amounts of these tetrahydrofuran derivatives in reasonable yields. 

Details of the oxidation and rearrangement of tabersonine (126) to (+)-14,15-dehydrovincamine (127) and (+)-14,15-dehydro-16-cp/-vincamine (128), which were previously recorded only in the patent literature, have now been published.90 A minor product in this sequence of reactions was formulated as (129), since hydrogenation, hydrolysis, and decarboxylation afford a hydroxy-amide (130), which can be reduced to rhazinilam (131) (Scheme 18). The reaction of 14,15-dehydrovincamine (127) with iodine and potassium iodate results in the formation of a dehydro-derivative (not isolated), followed by closure of the tetrahydrofuran ring. The product is the iodo-compound (132), which, as an iodo-enamine, loses its iodine when treated with acid, with formation of the alkaloid criocerine (133).90... 

We were able to direct the rearrangement 23—24 so that no disproportion into 9. and 30. occurred (13). The adducts 24 are stable and can now be used for hydroboration reactions whereby a suitable method for the elimination of triphenylphosphane from complex 24 must be used. This can be achieved with benzyl-iodide jjj. On a cIcTi-tion of the iodo compound 25 and an olefin 2 to a solution of 2 in tetrahydrofuran, the benzyl-triphenylphosphonium iodide precipitates and the free R-BH2 adds to the olefin 2 forming the tri-... 

The difference in reactivity between alkylated and acylated pentenyl glycosides can be rationalised as follows the elctrophilic iodonium ion will add to the double bond of the pentenyl moiety to give a cyclic iodonium ion. Nucleophilic attack by the oxygen will lead to an oxonium ion intermediate which then forms an oxocarbenium ion and an iodo-tetrahydrofuran derivative. The aglycone oxygen will be of low... 

Similarly, a catalyst (10 mol%) generated in situ from Cp2VCl2 and manganese/ chlorotrimethylsilane promotes a radical 5-exo cyclization of (1-iodo allylic ether 68 to tetrahydrofuran 69 in 62% yield (cf. Fig. 22) [153]. The reaction should proceed analogously to the corresponding Cp2TiCl2-catalyzed transformation. 

Intramolecular nucleophilic addition of alkoxides to vinyl sulfoxides (90) provided a route to (3-alkoxysuIfoxides (91) (Scheme 24). The cij-product was formed with up to 18 1 selectivity.58 Alkoxide nucleophiles undergo an addition/elimi-nation protocol with P-iodo vinyl sulfoxides to yield tetrahydrofurans and tetrahy-dropyrans, which contain either an endo- or an exo-cyclic double bond.59,60... 

The reaction of bis(dichloromethyl)zinc with mercuric chloride gives bis(dichloromethyl)mercury in 93% yield 262). The reaction of iodo-methylzinc iodide or bromomethylzinc bromide in tetrahydrofuran with an appropriate metal or organometallic halide was used in the preparation of (CH3)3SnCH2l, (CH3)3SnCH2Br, (CH3)2Sn(CH2l)2, (CHa) -... 

Substituted tetrahydrofuranes are cleaved selectively by this system at the less hindered carbon atom to afford y-iodo alcohols (equation I).-... 

Tetrahydrofurans can be synthesized by intramolecular substitution reactions. y-Bromo or iodo alcohols are common starting materials that readily cyclize under basic conditions. Tetrahydrofuran derivative 3 is obtained after radical coupling of iodide 1 with pent-4-en-l-ol... 

---