Spiro benzoxazole

Indolines, benzoxazole, and benzothiazole are possible as 2-methylene heterocycles. The number of known spirooxazine derivatives is much less than for the spiropyrans. This may be partly due to lack of many substituted o-nitrosonaphthols and partly due to lack of sufficient stability of spiro-oxazines. The structures of parent spirooxazines and the Xmax of their photomerocyanine forms are listed in Table 5. The Xmax of the colored forms of compounds 41-43 are not described in the literature. 

Reactions of 2-(3-hydroxy-3-phenylpropylseleno)benzoxazole with KH in tetrahydrofuran (THF) give selenetane 31. In the cases of /< rt-alcohols (R1 = C2H5 or CH2Ph), complex mixtures of products and no expected selenetane 31 are obtained because of steric hindrance at the reaction site. The formation of a selenetane is explained by a spiro intermediate which is converted into a selenolate anion. Intramolecular displacement of 30 gives the selenetane 31 (Scheme 7) <1998H633>. 

Benzoxazol 2-(l,l-Dimethy]-2-propenyl)- E8a, 1150 [Cl -> C(CH3)2-CH=CH2] lH-Carbazol 4a-Hydroxy-2,3,4,4a-tetrahydro- IV/lc, 483 Cyclobutan 1-Benzyl-l-cyan-3-hydroxy- E17e, 67 [(2-CN-ethyl) — oxiran + R —MgX] Cyclopentan-(spiro-2)-2,3-dihydro-indol - -3-oxo- VII/2a, 1051 Cyclopropan 2-Cyan-l-methoxy-2-methyl-l-phenyl- E17a, 764 (RO — CAr = Cr + En)... 

Treatment of IA with azomethines leads to 1,2-dihydroquinazolinones (198).261,262 With cyclohexanone anil (199), a spiro compound (201) is obtained however, five-, seven-, and eight-membered anils (200) gave only quinazolinediones (202)262 (Scheme 34). Benzoxazole (203) and IA do not form the expected tetracyclic adduct 204, but yield the quinazolinone 20598 by ring opening (Eq. 20). 

Treatment of 2-(phenacylthio)benzoxazole (333 R = Ph) with hydrazine hydrate results in cleavage of the oxazole ring and rearrangement via the spiro-intermediate (334) to the 677-1,3,4-thiadiazine (335) (Scheme 43). In contrast, the methyl analogue (333 R = Me) yields only the A-aminothiazole (336 86%) <82H(19)2119>. 

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