A Facile Synthesis of 2,4-Alkadienoic Esters and 2,4,6-Alkatrienoic Esters via Arsonium Ylides

Stereodefined and polyunsaturated inhibitors of histone deacetylase based on (2E,4E)-5-arylpenta-2,4-dienoic acid hydroxyamides

“…We sought to overcome all those problems by reaction of an aromatic aldehyde with a stabilised arsenic ylid (Scheme 1), the latter being known for achieving high (E)-selectivity. 13 Reaction of aromatic aldehydes 1b, 1c and 1e in THF with the ylid derived from 3-ethoxycarbonylallylidenetriphenylarsonium bromide, using 2.0 equiv K 2 CO 3 for 1b (7 days at 0°C then 10 min at 20°C) and 1.1 equiv n-BuLi for 1c and 1e (20 min at 0°C then 10 min at 20°C) afforded the corresponding dienic esters 3b (83%), 3c (51%) and 3e (81%). Treatment of esters 3b and 3c in methanol with a mixture of 50% aqueous hydroxylamine (10 equiv) and KOH (3.0 equiv) in methanol (addition at 0°C over 30 min followed by a further period at 0°C for 30 min, then stirring for 16 h at 20°C; procedure A) afforded the hydroxamic acids 4b (59%) and 4c (66%) after recrystallisation from ethyl acetate.…”

Efficient cleavage of the N–O bond of 3,6-dihydro-1,2-oxazines mediated by some α-hetero substituted carbonyl compounds in mild conditions

“…To a suspension of 3-ethoxycarbonylallylidenetriphenyl-arsonium bromide 23 (2.0 g, 4 mmol) in THF (10 mL) was added n-BuLi (2.5 M in hexanes, 1.6 mL, 4 mmol) dropwise at 0 • C. The red solution was stirred for 30 min at that temperature. 3-Bromobenzaldehyde (0.23 mL, 2 mmol) was then added and the reaction mixture was stirred for 1 h at 0 • C and 1 h at room temperature before being quenched with a saturated aqueous solution of NH 4 Cl.…”

“…Mp: 52-53 To a solution of triethyl phosphonocrotonate 23 (1.46 mL, 6.6 mmol) and 4-nitrobenzaldehyde 29 (1.0 g, 6.6 mmol) in THF (11 mL) was added molecular sieves (powdered 4 A ˚, 1.0 g) and LiOH•H 2 O (0.29 g, 6.9 mmol) under vigorous stirring. The suspension was warmed at 45 • C for 10 min, cooled to room temperature, filtered through Celite R and rinsed thoroughly with diethyl ether.…”

Olefination of carbonyl compounds: modern and classical methods

“…91 Thus the ylide 118 derived from the ethyl 4-bromocrotonate 119 is used in the stereoselective synthesis of alka-2,4-dienoates 120 and 2,4,6trienoates 121. 92 Arsenic ylide 122, the reaction product of triphenylarsine and bromoacetaldehyde 123, reacts with phthalic aldehyde in the presence of potassium carbonate, to give the a,b-unsaturated aldehydes 124 in high yields; the nature of the carbonyl components can be varied over a broad range. This reaction is stereoselective; the ratio of the E-and Z-isomers of the target alkenes is no less than 97 : 3.…”