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Cholestenone. The literature method7 was modified by using aluminum isopropoxide in place of aluminum terf-butoxide. A solution of 21 g of freshly distilled aluminum isopropoxide in 130 mL of benzene was added to a solution of 30 g of cholesterol in 350 mL of benzene and 250 mL of acetone. After the mixture was refluxed for 48 h, the product was isolated as described7 to give 18 g of cholestenone, mp 80-81.5 °C (lit.7 mp 78.5-80.5 °C).The filtrate was subjected to recycling which raised the overall yield to 85-90%. 24-Hydroxychol-4-en-3-one Acetate (I). Cholestenone (0.50 g) was dissolved at 0 °C in a solution of 19.5 mL of CF3COOH, 10.5 mL of 96% H2SO4, and 1.0 mL of 50% aqueous H202. After being stirred for 4 h at 0 °C, the solution was quenched by slow addition to ice-water. A hexane extract was washed with 5% NaHC03 and dried over MgS04.After removal of solvent in vacuo at 25 °C, the residue was dissolved in a solution of 50 mL of acetic acid, 2 mL of water, and 1.0 g of sodium acetate. The solution was refluxed for 18 h under N2, cooled, and diluted with 100 mL of water. A hexane extract was washed with 5% Na2C03 and dried over MgS04. Removal of solvent in vacuo at 25 °C gave 0.15 g of crystalline acetate (I). A GC analysis indicated that it was 70% pure with the remainder being unreacted cholestenone.The impure I was chromatographed on 10 g of 28-200 mesh silica gel, using 65:35 hexane-ether. Cholestenone eluted before

Collisionally activated dissociation of deprotonated aromatic sulfonic acids in the gas phase causes rearrangement and fragmentation to produce the corresponding phenoxide ions. The mechanism for this reaction has been investigated and the results of this study favor initial intramolecular nucleophilic addition of a sulfonate oxygen atom to the aromatic ring, a process which is followed by heterolytic cleavage of the carbonsulfur bond to rearomatize the ring. The product from this addition4imination sequence is the anion of a sulfurous acid halfester, which loses SO, to generate the corresponding phenoxide ion. 2 R = SOJH 3 R = SO,H

Y) was treated with a solution of iodine in ether. The course of the reaction was followed by gas chromatography at 65"; results are in Table IY. Iodine decolorization was very rapid, but at 0.5 ml of iodine the color persisted.Reaction with Bromine. A solution of 8.69 mmol of VI in 21.4 ml of isooctane was treated with a solution prepared from 1 ml (18 mmol) of bromine in 100 ml of carbon tetrachloride. After 60 ml had been added, the color of the bromine persisted, indicating that about 10 mmol had reacted. The mixture contained much yellow solid, which was filtered off and washed with isooctane. The solid was dissolved in water and neutralized with sodium bicarbonate.The solution was saturated with potassium sulfate and extracted several times with chloroform. Extracts were combined, dried over Drierite, and evaporated to leave 0.932 g of solid. The crude product contained residual bromide ion (positive test with aqueous silver nitrate). It reduced potassium permanganate solution. Its infrared spectrum showed stretching bands for C=C (1570 cm-I), olefinic C-H (3030 cm-l), and phosphoryl (1200 cm-l).Reaction with Oxygen. The absorbance at 284 mM of a saturated water solution of VI in a quartz cell sealed with wax was measured over a period of 6.5 hr. The log of the absorbance decreased in a roughly linear fashion from 0.1858 to 0.1098. When the stopper was removed from a solution of log A 0.1098, the absorbance dropped much more rapidly and vanished on long standing. Only end absorption was present in the spectrum.Abstract: A photochemical transformation of barrelene was observed, wherein a C s H~ isomer is produced as the major product; cyclooctatetraene was obtained as a minor product. The structure of the CsHs isomer was elucidated as that of bullvalene minus one vinyl bridge, and the compound was named "semibullvalene." The process was demonstrated to proceed cia the triplet of barrelene in a process subsequently shown to be general. The irradiation of semibullvalene afforded cyclooctatetraene. It was found that semibullvalene undergoes degenerate valence tautomerism at a faster rate than any previously studied system. Barrelene was labeled at all vinyl positions with deuterium, leaving only the bridgehead positions still bearing hydrogen. The method developed for deuteration of barrelene involved treatment with lithium N-deuteriocyclohexylamide in N,N-dideuteriocyclohexylamine; the method promises to be generally useful for preparing deuterated compounds. The location of the hydrogen label in the semibullvalene photolysis product was investigated and found to fit one of two reasonable mechanisms. The reaction mechanism was shown to proceed oia a unique bicyclic, allylic, triplet biradical having finite lifetime. The rearrangement was considered from a theoretical viewpoint with the use of three-dimensional Hiickel theory, and the results were used to correlate the excited-state potential energy surface with observed photochemical behavior. nterest in our laboratory has been heavily focused on

A new method is described for regioselective partial deprotection of carbohydrates protected as benzylidene acetals. This deprotection was accomplished for each of the six methyl pyranosides (4, 5, and 18-21) studied by irradiation of the protected sugar and .¡V-bromosuccinimide (NBS) in the presence of water. Under these conditions the benzylidene (1,3-dioxolane) ring in each compound opened to give a methyl pyranoside with an axial benzoyloxy group and an equatorial hydroxy group. For example, irradiation of methyl 3,4-O-benzylidene {R or S)-6-deoxy-2-0-(2,2-dimethylpropanoyl)-a-L-galactopyranoside (18 or 19) with NBS, barium carbonate, and water resulted in the formation of methyl 4-0-benzoyl-6-deoxy-2-0-(2,2-dimethylpropanoyl)-a-L-galactopyranoside ( 22) in 72% yield. In a similar manner compounds 4 and 5 gave 10 and compounds 20 and 21 produced 23. The advantages of this deprotection process are described.

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