Search

A novel sulfenylation method induced by aromatization of quinone mono-O,S-acetals is described. These sulfenylation reagents readily react with silyl enolethers or electron rich aromatic compounds to give sulfenylation products under mild conditions. In particular, O,S-acetal 2j, which possesses a pentafluorophenylthio function, is the most effective reagent from the standpoint of the adaptability for various substrates.

Optically pure (5R)- [and (5S)]-5,6-dihydro-5-phenyl-2H-1, 4-oxazin-2-one N-oxides [(5R)- and (5S)-2] were designed as chiral (E)-geometry-fixed alpha-alkoxycarbonylnitrones 1. The nitrones (5R)- and (5S)-2 were synthesized by three-step oxidation of (R)- and (S)-phenylglycinols [(R)- and (S)-3], condensation of the resulting (R)- and (S)-2-hydroxylamino-2-phenylethanols [(R)- and (S)-5] with glyoxylic acid, and cyclization of the intermediary nitrones (R)- and (S)-6b. The nitrone (5R)-2reacted with olefins 7-14 under mild conditions to afford the corresponding cycloadducts 15-22 as the main products via the least sterically demanding exo modes. Cycloadduct 30 obtained from (5S)-2 and cyclopentadiene was effectively elaborated to (1S,4S, 5R)-4-benzyloxycarbonylamino-2-oxabicyclo[3.3.0]oct-7-en-3-one (28), the key synthetic intermediate of carbocyclic polyoxin C.

Efficient synthesis of α - C -glycopyranosides through a radical addition reaction using 2,2′-azobis(2,4-dimethyl-4-methoxyvaleronitrile) [V-70] as an initiator under mild condition was developed. This method made it possible to completely control the stereocenter at the anomeric position and obtain only the α-anomer in high yield compared with AIBN, Et 3 B, and photo irradiation methods.

(R)-5,6-Dihydro-5-phenyl-1,4-oxazin-2-one N-oxide {(R)-2} reacts with allyl alcohols 3a-c in the presence of magnesium bromide from the less hindered face via exo-mode to afford corresponding cycloadducts 4a-c with excellent stereoselection. Treatment of (R)-2 with three equivalents of racemic secondary allyl alcohols 3d-g under the same conditions causes partial kinetic resolution to give 4d-g as main products among eight possible stereoisomers. Cycloadduct ent-4a from (S)-2 and 3a was converted directly to g-lactone 6, which is known as the key synthetic intermediate of antibiotic clavalanine.

Radical addition reactions of bromomalononitrile to various alkenes using 2,2‘-azobis(2,4-dimethyl-4-methoxyvaleronitrile) (V-70) were examined. The advantages of V-70 which is an effective radical initiator at low temperature in contrast to the other azobis compounds are described. Especially V-70L (the low melting point diastereomer) was found to be the best radical initiator.

α-Linked C-glycopyranosides were obtained effectively by the radical addition reaction using V-70, an effective radical initiator under mild conditions.

The attributes of 2,2′-azobis-(2,4-dimethyl-4-methoxyvaleronitrile) (V-70), which is an effective radical initiator at low temperature, in contrast to 2,2′-azobisisobutyronitrile (AIBN) are described.

Ethoxy vinyl esters (EVE:2) were efficient reagents for promoting the asymmetric Pummerer reaction with high enantioselectivity and high yield in contrast to the generally used acid anhydrides. Increasing the electron-donating ability on the R function in EVE 2 tended to increase enantioselectivity. Consequently, effective asymmetric rearrangements were achieved using EVEs 2b,c bearing a methoxybenzoyloxy function.

Treatment of α-methoxycarbonylnitrones with 5 equiv. of allyl alcohols in the presence of 1 equiv. of titanium tetraisopropoxide causes tandem transesterification, E , Z -isomerization of the nitrone moieties, and intramolecular cycloaddition to afford bicyclized compounds in one step. To reduce amounts of allyl alcohol, combined use of a catalytic amount of titanium tetraisopropoxide and molecular sieves 4A was found to be a more improved catalytic system. It was also found that reactions of ( Z )-allyl alcohols with α-methoxycarbonylnitrone are more facile than those of ( E )-allyl alcohols. This aspect was extended to geometry differentiated cycloaddition.

Ethoxy vinyl esters (EVE:2) were efficient reagents for promoting the asymmetric Pummerer reaction with high enantioselectivity and high yield in contrast to the generally used acid anhydrides. Increasing the electron-donating ability on the R function in EVE 2 tended to increase enantioselectivity. Consequently, effective asymmetric rearrangements were achieved using EVEs 2b,c bearing a methoxybenzoyloxy function.

The attributes of 2,2′-azobis-(2,4-dimethyl-4-methoxyvaleronitrile) (V-70), which is an effective radical initiator at low temperature, in contrast to 2,2′-azobisisobutyronitrile (AIBN) are described.

α-Linked C-glycopyranosides were obtained effectively by the radical addition reaction using V-70, an effective radical initiator under mild conditions.

(R)-5,6-Dihydro-5-phenyl-1,4-oxazin-2-one N-oxide {(R)-2} reacts with allyl alcohols 3a-c in the presence of magnesium bromide from the less hindered face via exo-mode to afford corresponding cycloadducts 4a-c with excellent stereoselection. Treatment of (R)-2 with three equivalents of racemic secondary allyl alcohols 3d-g under the same conditions causes partial kinetic resolution to give 4d-g as main products among eight possible stereoisomers. Cycloadduct ent-4a from (S)-2 and 3a was converted directly to g-lactone 6, which is known as the key synthetic intermediate of antibiotic clavalanine.

A novel sulfenylation method induced by aromatization of quinone mono-O,S-acetals is described. These sulfenylation reagents readily react with silyl enolethers or electron rich aromatic compounds to give sulfenylation products under mild conditions. In particular, O,S-acetal 2j, which possesses a pentafluorophenylthio function, is the most effective reagent from the standpoint of the adaptability for various substrates.

A novel method for sulfenylation induced by aromatization of quinone mono-O,S-acetals is described.

The 1,3-dipolar cycloaddition of (R)-5,6-dihydro-5-phenyl-2H-1,4-oxazin-2-one N-oxide[(5R)-2], a chiral and geometry fixed α-alkoxycarbonylnitrone, with alkenes 3–6 proceeded smoothly to afford cycloadducts 7–10 as main products viaβ-exo mode.