For 1,3-oxathiolane

In contrast, 1,3-oxathiolanes give a substantial molecular ion and a small [M — 1] ion. Fragments tend to retain sulfur and for 1,3-oxathiolane itself the loss of CH2O is the base peak, the carbon atom being derived from the 2-position (720MS(6)415). 

Data for 1,3-oxathiolane and 2-substituted derivatives were included in CHEC-I <84CHEC-i(6)749> but this is extended to other substitution patterns as well as to oxathiolanones, oxathiolanethiones and oxathiolane 3,3-dioxides in Table 3. 

The most commonly used protected derivatives of aldehydes and ketones are 1,3-dioxolanes and 1,3-oxathiolanes. They are obtained from the carbonyl compounds and 1,2-ethanediol or 2-mercaptoethanol, respectively, in aprotic solvents and in the presence of catalysts, e.g. BF, (L.F. Fieser, 1954 G.E. Wilson, Jr., 1968), and water scavengers, e.g. orthoesters (P. Doyle. 1965). Acid-catalyzed exchange dioxolanation with dioxolanes of low boiling ketones, e.g. acetone, which are distilled during the reaction, can also be applied (H. J. Dauben, Jr., 1954). Selective monoketalization of diketones is often used with good success (C. Mercier, 1973). Even from diketones with two keto groups of very similar reactivity monoketals may be obtained by repeated acid-catalyzed equilibration (W.S. Johnson, 1962 A.G. Hortmann, 1969). Most aldehydes are easily converted into acetals. The ketalization of ketones is more difficult for sterical reasons and often requires long reaction times at elevated temperatures. a, -Unsaturated ketones react more slowly than saturated ketones. 2-Mercaptoethanol is more reactive than 1,2-ethanediol (J. Romo, 1951 C. Djerassi, 1952 G.E. Wilson, Jr., 1968). 

For 1,3-dithiolanes the ring is flexible and only small energy differences are observed between the diastereoisomeric 2,4-dialkyl derivatives. The 1,3-oxathiolane ring is less mobile and pseudoaxial 2- or 5-alkyl groups possess conformational energy differences (cf. 113 114) see also the discussion of conformational behavior in Section 4.01.4.3. 

For(n = 3) Me2CH(CH2)20N0, CH2CI2, reflux, 2.5 h, 65% yield. 1,3-Oxathiolanes are also cleaved by isoamyl nitrite. 

Smaller aldehydes form cyclic acetal-type oligomers readily in aqueous conditions.60 Diols and polyols also form cyclic acetals with various aldehydes readily in water, which has been applied in the extraction of polyhydroxy compounds from dilute aqueous solutions.61 E in water was found to be an efficient catalyst for chemoselective protection of aliphatic and aromatic aldehydes with HSCH2CH2OH to give 1,3-oxathiolane acetals under mild conditions (Eq. 5.7).62... 

For preparative purposes, the reaction of thiocarbonyl ylides with carbonyl compounds can be considered as an alternative method for the synthesis of 1,3-oxathiolanes. Aromatic aldehydes, chloral, glyoxalates, mesoxalates, pyruvates as well as their 3,3,3-trifluoro analogues are good intercepting reagents for thioketone (5)-methylides (36,111,130,163). All of these [3 + 2] cycloadditions occur in a regioselective manner to produce products of type 123 and 124. 

The desUylation strategy has been used for the cycloaddition of the parent thiocarbonyl yhde la with aldehydes and reactive ketones. The product obtained using A-methyl-3-oxoindolinone as the trapping agent corresponds to the spiro-cyclic compound 125 (168). Thioketene (5)-methylide (127) was reported to react with aromatic aldehydes and some ketones to furnish 2-methylene-substituted 1,3-oxathiolanes (128) (51) (Scheme 5.42). 

Heating cyclic mono-, di- or tri-thiocarbonates, usually in the presence of base, gives thiiranes and carbon dioxide, carbon oxysulfide or carbon disulfide respectively. The methiodide salts of 2-methylimino-l,3-oxathiolanes are converted to thiiranes with high stereoselectivity, except for 5-aryl-substituted oxathiolanes (Scheme 146) (80LA1779). Flash vacuum thermolysis of l,3-oxathiolan-5-ones causes loss of carbon dioxide and nearly quantitative formation of thiiranes of inverted configuration (Scheme 147) (80JA744). For example, thermolysis of c/s-2,4-diphenyl-1,3-oxathiolan-5-one gives trans-2,4-diphenyl-thiirane. 

In the October 10, 1988 issue of Chemical Engineering News there appeared a brief report from the Israel Institute for Biological Research about an acetylcholine analog, cis-2-methylspiro(1,3-oxathiolane-5,3 )quinuclidine, which seems to be very specific for brain Ach receptors involved in AD. In the same report another drug in Phase I clinical trials was mentioned. Produced by Bristol-Myers it is meant to be used for a variety of cognitive memory disorders including AD. 

Oxathiolanes (11) are formed from aldehydes and ketones by reaction with 2-mercaptoethanol (HS-CH2-CH2OH) in the presence of, for example, zinc chloride-sodium acetate in dioxane solution at room temperature,139 or boron trifluoride-etherate.140 They are more stable to an acidic medium than the 1,3-dithianes, and therefore may be the protective group of choice in certain instances. 

Deprotection of 1,3-oxathiolanes may be effected in a buffered medium in the presence of either mercury(n) chloride or with Raney nickel,141 or very conveniently with Chloramine-T.142 In this latter deprotection reaction, 1,4-oxathiaspiro[4.4]nonane (12) affords cyclopentanone in 91 per cent yield when treated for 2 minutes with Chloramine-T in 85 per cent methanol-water at... 

There has been no effort to study systematically a series of compounds. The lower dioxoles and oxathioles are liquids, insoluble in water but soluble in most organic solvents. 1,3-Dioxole boils at 51 °C at atmospheric pressure, while 2,2-dimethyl substitution raises this to 72-73 °C. No boiling point has been reported for 1,2-dioxolane and the only report for 1,2-oxathiolane indicates that it codistills with chloroform at 20 °C (0.1 mmHg). 1,3-Dioxolane boils at 75 °C (760 mmHg) and the introduction of sulfur raises the boiling point such that 1,3-oxathiolane boils at 132-136 °C (760 mmHg). 

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