Ring synthesis 7- hydroxy

Acetyl- and 5-formylisothiazoles are readily available from 5-lithioisothiazoles.71,102 However, 3-methyl-4-nitroisothiazole does not form a lithium derivative,72 and 4-formyl-3-methyl-4-nitro-isothiazole was prepared by reduction of the appropriate acid chloride with lithium tri-Lbutoxyaluminum hydride.140 A 5-formyl-4-hydroxy-isothiazole has been prepared by direct ring synthesis [Eq. (12)].29... 

The oxidation of indolines with sodium tungstate/hydrogen peroxide both aromatises and also oxidises the nitrogen, resulting in 1-hydroxy-indoles. 1-Hydroxy-indoles can also be obtained via ring synthesis involving lead-promoted reductive cyclisation of ortfto-nitrobenzyl-ketones (or -aldehydes)." ... 

Diketones from hydroxy-a,j -ethyleneketones via diols—Robinson hydro-phenanthrene ring synthesis s. 16, 871... 

Hydroxypyridone ring synthesis. 80 g. phenothiazine, diethyl n-butylmalonate, and unglazed clay plate fragments heated 22 hrs. at 277° crude l-keto-2-n-butyl-3-hydroxy-lH-pyrido[3,2,l-kl]phenothiazine. Y 73%.—Clay plate catalyzes this reaction and particularly prevents decreasing yields of larger batches. F. e., also with phenoxazine, s. M. Harfenist et al., J. Org. Chem. 27, 3977 (1962). 

Rearrangements of epoxides and their derivatives under the presence of Lewis acids are valuable tools in the synthesis of carbonyl compounds. Kita and coworkers have recently shown that the rearrangement of six membered 2,3-epoxy alcohols (45) in the presence of nonchelating Lewis acids such as BF3 OEt2 gave the 5-membered ring P-hydroxy ketone (46). In contrast, the same reaction under the influence of SnCU gives a six membered a-hydroxy ketone (47) (Equation 30) [32]. 

Coumarin is usually prepared by heating salicylaldehyde with acetic anhydride and sodium acetate (i.e., the Perkin cinnamic acid synthesis, p. 23 6), whereby the 0" hydroxy-cinnamic acid (I) undergoes cyclisation to coumarin. Coumarins having substituents in the benzene ring can often be similarly prepared. 

The stereospecific synthesis of an A ring synthon of la-hydroxy vitamin D has been carried out. The ( )-allcene is cyclized to give the (E -c.xo-diene 155, and the (Z)-allcene affords the (Z)-e,xo-diene 156 stereospecifically[125,126]. These results can be understood by the cis addition and syn elimination mechanism. 

P-Hydroxy acids lose water, especially in the presence of an acid catalyst, to give a,P-unsaturated acids, and frequendy P,y-unsaturated acids. P-Hydroxy acids do not form lactones readily because of the difficulty of four-membered ring formation. The simplest P-lactone, P-propiolactone, can be made from ketene and formaldehyde in the presence of methyl borate but not from P-hydroxypropionic acid. P-Propiolactone [57-57-8] is a usehil intermediate for organic synthesis but caution should be exercised when handling this lactone because it is a known carcinogen. 

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