Inter‐ and intramolecular hetero‐Diels‐Alder reactions, 37. Syntheses of the 3‐amino sugar glycosides rac‐4‐deoxydaunosaminide rac‐4‐deoxyristosaminide, and rac‐acosaminide

Abstract

The hetero‐Diels‐Alder reaction of the phenylthio‐activated N‐monoacyl‐ and N,N‐diacyl‐enamino ketones 8a‐c containing a methyl group at position 2 of the oxadiene with the electron‐rich dienophiles 9a‐c yields the exo/endo adducts 10a‐d and 11a‐d in 82–95% yield with the endo adducts as the main products. The enamino ketone 8d with a S‐ethyl group at C‐3 does not react. Hydrogenation of 11a with Raney nickel in THF leads to the desulfurized dihydropyran 12, whereas in MeOH gives stereoselectively the perhydrophthalimido derivative 13, which, after deprotection, yields the β‐methyl glycoside 14 of rac‐4‐deoxydaunosamine. Under similar conditions 10c is converted into the β‐ethyl glycoside 15 of rac‐N‐benzoyl‐4‐deoxyristosamine. Stereoselective hydroboration of 12 affords 17 and subsequent cleavage of the protecting group leads to the β‐methyl glycoside 18 of rac‐acosamine.

Synthesis of 3,4-dihydro-2H-pyrans by hetero-Diels–Alder reactions of functionalized α,β-unsaturated carbonyl compounds with N-vinyl-2-oxazolidinone

“…Also the influence of phenyl, 4-nitrophenyl or 4methoxyphenyl groups present in enones on diastereoselectivity and yields of products was compared. Compounds 1a-d 28,32 and 1e-g [33][34][35] were obtained according to the methods described in literature. They exist mainly as E isomers with s-Z conformation, which is suitable for Diels-Alder cycloaddition.…”

Syntheses of Both Enantiomers of 1,7-Dioxaspiro[5.5]undecane: Pheromone Components of the Olive Fruit-Fly Dacus oleae from a New Chiral Intermediate, the (SS)-2-(p-Tolylsulfinyl)prop-2-en-1-ol

“…Raney nickel in methanol 12 involving reduction of the C=C bond and desulfurization affords (+)-(S)-2 and (-)-(R)-2 in 62 and 60% yield, respectively (Scheme 2). The spectral properties of the synthetic products are in accordance with those reported in the literature.…”

“…The spectral properties of the synthetic products are in accordance with those reported in the literature. 5,6 (R)-1,7-Dioxaspiro[5.5]undec-2-ene (8) is obtained in 69% yield by treatment of (S S , 6R)-7 with Raney nickel in anhydrous tetrahydrofuran 12,13 (Scheme 3).…”

Synthesis of Phenylthio Substituted 4H-Pyrans and 2-Pyridinones by Conjugate Addition-Cyclization of CH-Acids to α,β-Unsaturated Ketones

“…Phenylthioacetone [5], 4-N,N-dimethyl)-3-phenylthio-3-buten-2-one [14], and 4-aryl-3-phenylthio-3-buten-2-one [13] were synthesized according to procedures described in the literature.…”