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Oxidation of benzohydroxamic acid with tetraethylammonium periodate in the presence of the conjugated diene thebaine (1 ) gave the cycloadduct 6~,14~-(N-benzoylepoxyimino)-6,14-dihydrothebaine (2; R = Ph), in high yield. The corresponding N-acetyl derivative (2 ; R = Me) was prepared similarly using acetohydroxamic acid. Likewise, 2-benzoyl-and 2-acetyl-3,6-dihydro-2H-1,2-oxazine (5; R = Ph) and (5; R = Me) were obtained from buta-l,3-diene, and the N-benzoyl and N-acetyl derivatives of 9,l O-epoxyimino-9,l O-dihydro-9,l O-dimethylanthracene (6; R = PhCO) and (6; R = Ac) from 9,lO-dimethylanthracene (DMA). These reactions are believed to involve the formation of nitrosocarbonylbenzene or nitrosocarbonylmethane, representatives of a new class of transient, reactive species. The cycloadduct (6 ; R = Ac) decomposed in benzene at 60 "C in the presence of thebaine (1) to give the thebaine adduct (2; R = Me) and DMA. First-order kinetics were observed for the release of DMA, consistent with slow dissociation of the adduct (6; R = Ac) followed by rapid capture of nitrosocarbonylmethane by thebaine. The related adduct (6; R = PhCO) behaved similarly. DMA adducts of the type (6) are valuable in studies on the reactions of nitrosocarbonyl compounds, especially with co-reactants sensitive t o oxidation. Thus (6 ; R = Ac) and 1,3-diphenylisobenzofuran (7) reacted cleanly in benzene at 80 "C to give the O-acetyloxime (1 0) of 1,2-dibenzoylbenzene, possibly via the N-acetylnitrone (9) derived from the initially formed cycloadduct ( 8 ) .NITROSYL cyanide (O=N-C-N) undergoes Diels-Alder reactions with conjugated dienes to form 2-cyano-3,6-dihydr0-2H-l,2-oxazines.l~~ I t appears that the electron-withdrawing cyano-group enhances the dienophilic character of the C-nitroso-group while presenting minimal steric hindrance to cycloaddition. that compounds of the general class XC(=Y)NO, where Y may be an electronegative element 0, N, or S, should also be reactive, electron-demanding dienophiles. We describe here the formation and reactions of C-nitrosocarbonyl compounds, the first members of this new class (X = C c ; Y = 0) of transient specie^.^ C-Nitrosocarbonyl compounds had been proposed several times prior to our studies as possible intermediates in organic reactions, viz. in the pyrolysis of mixtures of nitrite esters and aldehyde^,^ in the pyrolysis of azidoformates in dimethyl sulphoxide,6 and in the oxidation of hydroxamic acids with sodium periodate, iodine, Nbromosuccinimide, or potassium ferricyanide or with dicyclohexylcarbodi-imide and phosphoric acid.8 In none of these studies were the proposed intermediate species, RCONO or ROCONO, observed directly and, in

The effects of ring substitution on the color stability of a group of 14 synthetic 3-deoxyanthocyanidins have been studied. In acid solution (pH 2.8), none of the synthetic analogues prepared show significant advantages in overall performance over the naturally occurring apigeninidin (2). At pH 7.0, however, the presence of a carboxylate group at C4 results in unusually stable colorants.The anthocyanins are naturally occurring red pigments having the basic structure 1 (Timberlake and Bridle, 1975, R .