From Vinylallenes to Ketones of the Dihydrojasmone Type

2-Methyl-4,5-dihydroimidazole as a doubly nucleophilic unit: preparation of dihydroimidazole azaprostanoids

“…7729) eluting with chloroform-methanol (97: 3 v/v) to give the C-acylated material l-benzyl-2-(7-bromo-2-hydroxyhept-lenyl)-4,5-dihydroimidazole (5a) (0.27 g, 33%) (Found M + , 350.100. C1 7H23N2079Br requires M, 350.099); v,,,(CHCl,) 3 600-2 700, 1 600, 1 530, 1455, and 1 140 cm-'; 6(90 MHz) (19), 216 (16), 201 (42), 174 (18), 173 (23), 91 (loo), and 74 (10).…”

“…7734,120 g), eluting with chloroform-2-aminopropane (97: 3 v/v), gave the title compound (1.29 g, 73%) (Found C, 63.86; H, 9.55; N, 9.31%; M', 296.2100. C16H28N203~0.25H20 requires C, 63.86; H, 9.55; N, 9.31%; M , 296.2100); v,,,(film) 3 280 (water), 2 930, 2 870, 1 610, 1 425, 1 398, 1 272, 1 193, 1060,994,945, and 765 cm-'; 6(90 MHz) 0.87 (3 H, s, CH,CCH3), 1.20-1.90 [lo H, m, (CH,),C], 1.96 (3 H, s, NSCH,), 3.0-3.90 (6 H, m, NCH2CHzN and NCH2-CH,C), and 3.98 (6 H, s, 3 x OCH,); m/z 296 (M'), 295 (27%), 267,265 (19), 168, 125,111,98,97 (loo), 84 (14), 56 (77), and 55 (20).…”

“…We report here the synthesis of the key intermediate (13) in the proposed sequence by elaboration, using the methodology developed above, of 2-methyl-3a,4,7,7a-tetrahydrobenzimidazole (14), itself prepared from the cyclic urea underwent thermolysis and Curtius rearrangement in situ to afford the isocyanate (18) (89%), from which the isatoic anhydride (19) was obtained (85%) by silyl ester cleavagecyclisation in water (O' C, 2 days). 13 The reaction of trimethylsilyl azide with the anhydride (19) as above led to a second Curtius rearrangement and the production of mixtures of the required cyclic urea (15) (3040%) and its N-trimethylsilylox ycarbonyl precursor (20). After much investigation, our optimised protocol for the production of the imidazolone (15)…”

The chemistry of bisallenes

“…Applying the mechanism discussed in this latter context to 24 , it is reasonable to propose the formation of an allene-epoxide first [141], which can exist either in a transoid , 212 , or cisoid conformation, 213 (Scheme 51). Whereas the former could open up to the “stretched” zwitterion 214 , which by carboxylate interception would lead to 210 , the more “closed” allenoxide 213 could isomerize to 215 , which on ring closure would furnish 209 and 211 , respectively.…”

The preparation of allenes and cumulenes

“…Section II.B.3).In that year the parent hydrocarbon 509 was prepared: the dibromoketone 506 -H2C=C=C=C=CH2 4 HCEEC-CEC-CH3(178) was converted by the DMS approach to the allenic alchol 507, which on treatment with aluminum oxide oxide under carefully controlled conditions yielded ;he vinylallene 508. When the latter is submitted to flash vacuum pyrolysis (700 C, 1 (r3 torr) anthracene is split off, and a mixture of 1,2,3,4-~entatetraene (509) and 1,3-pentadiyne (510) is produced in 85% yield (equation 178)838 *8039.…”