Electron deficient heteroaromatic ammonioamidates. Part 24. N-(Quinazolin-3-io)amidates. Part 11. The photochemistry of N-(6,7-methylenedioxyquinazolin-3-io)amidates in acetone

Abstract

N-(Quinazolin-3-io)amidates (1) may exist, depending on the nature of the groups R, R1, and R2, and in the absence of nucleophiles, as equilibrium mixtures of the monomeric (1) and dimeric (3) forms. For the first time evidence has been found for the generation of photoproducts of the dimeric forms (3) via irradiation of the quinazolinioamidates (1 a-c) in acetone in which substantial amounts of the dimers (3a-c) are present. Thus, the quinazolinioamidates (1 ) are the only heteroaromatic ammonioamidates which are known not only to exist in three forms, viz. the monomer, the adducts (2), and the dimers ( 3 ) , but also to furnish characteristic photoproducts of all three forms.Of the electron deficient heteroaromatic N-ammonioamidates studied so far the N-(quinazolin-3-io)amidates (1) are the only ones which (to a greater or lesser degree, depending on the nature of the ligands R, R1, and R2, as well as the Nu group) are able to form adducts (2) with nucleophiles HNu and, in the absence of such nucleophiles, dimers (3), 4-8 As a consequence, the photochemistry of compounds (1) is more complicated than that of other ammonioamidates. In the presence of nucleophiles (e.g. alcohols,6 toluene-a-thiol,' amines,8 and acetamide *) two series of characteristic photoproducts, originating from forms (1) and (2), respectively, are formed.Here we report the photochemistry of a series of N-(quinazolin-3-io)amidates (la-h) 5 in acetone; this solvent, in the absence of acidic and basic catalysts,' is unable to form type (2) adducts, viz. (1 3), with the amidates. Compounds (la-h) were irradiated in acetone under argon with a highpressure mercury immersion lamp (HPK-125) through Pyrex. Chromatographic work-up of the resulting mixtures furnished the photoproducts (4)-(13) ( Table l).T The majority of the photoproducts had been obtained previously on irradiation of compounds (la-h) in the presence of nucleophiles as shown in Table 2. On the other hand, compounds (9h), (1 1 a-c), and (1 2e) are novel and such products have not been obtained before on irradiation of heteroaromatic ammonioamidates. Compounds (7d) and (7h) are also new. (For proof of the structures of the new compounds, see below.) t For a review on the chemistry of N-(quinazolin-3-io)amidates and related compounds with special emphasis on their photochemistry (see ref. 3). $ Compounds of this type are correctly named as ' amidides '; they are so named in the Experimental section.3 Compounds ( l a -c ) exist in the crystalline state as the pure dimer (3a) and as mixtures of the momers (lb), (lc) and the dimers (3b), (3c), respectively. However, in CDC13 solution equilibria between the monomeric and dimeric forms are rapidly e~tablished.~ This has been shown to be the case for the amidate (1 b), and may be assumed for the amidates (la) and (ic) in solvent acetone as well. It is, thus, immaterial whether monomers or dimers are actually introduced as the starting materials in the (a)-(c) series. 7 Although irradiation was continued until no unchanged starting compounds we...

Basicity-Tuned Reactivity: diaza-[1,2]-Wittig versus diaza-[1,3]-Wittig Rearrangements of 3,4-Dihydro-2H-1,2,3-benzothiadiazine 1,1-Dioxides

“…The formation of compounds 3 is particularly noteworthy since [1,3]-rearrangements involving a N–N bond cleavage and inclusion of a C 2 unit are very rare in the literature and occur with a different mechanism. − The targeted synthesis of 1,2-benzothiazine 1,1-dioxides 3a – f was finally conducted with 6 equiv of t -BuOK (Scheme ), by crystallization either in DMSO ( 3a – c ) or in THF ( 3d – f ), yielding the products in a pure form even without chromatographic purification. Contrary to the other reactions taking place at room temperature, the quenched reaction mixture of 4-ethyl derivative 1b had to be heated to reflux to cyclize to 3b (trans–cis diastereomeric ratio = 97:3).…”