Zhijie Ni

SYNTHESIS OF NOVEL BICYCLIC NITROGEN HETEROCYCLES BY THE INTRAMOLECULAR DIPOLAR CYCLOADDITION REACTION OF NITRONES WITH ALLENES AND ALKYNES

Abstract A study of the intramolecular dipolar cycloaddition reactions of a series of allenyl and alkynyl nitrones has been carried out. Phenylhydroxylamine readily reacts with o -(1,2-propadienyloxy)benzaldehyde to give a dioxaazabicyclo[3.2.1]octene. The intramolecular 3+2-cycloaddition of 2-(1,2-propynyloxy)benzaldehyde and N-methylhydroxylamine was also studied. In this case, the major cycloadduct formed was identified as 4-methyl-2,5- endo -oxo-2,3,4,5-tetrahydro[1,4]benzoxazepin. The formation of this novel rearranged product involves an initial dipolar cycloaddition across the acetylenic π-bond to give the expected 4-isoxazoline as a transient intermediate. The next step proceeds by homolysis of the O-N linkage and this is followed by ring closure to produce an aziridine which undergoes further C-C bond cleavage. The resulting azomethine ylide is converted to the final rearranged product by means of an ortho -quinone methide intermediate. Phenylsulfonyl activated allenes were also found to react with alkylhydroxylamines to give nitrones which undergo cycloaddition with the neighboring π-bond to afford the resulting bicyclic nitrogen heterocycles.

Intramolecular [3+2]-cycloaddition of nitrones with allenes and alkynes

Abstract The intramolecular dipolar cycloaddition reactions of allenyl and alkynyl nitrones proceed smoothly to give high yields of cycloadducts.

Cycloaddition reactions of unsaturated sulfones

The reaction of a series of allyl-substituted bis(phenylsulfony1)- methanes or dimethyl malonates with 2,3-bis(phenylsulfonyl)- l13-butadiene in the presence of base afforded alkenyl-substituted allenes in good yield. The reaction proceeds by initial attack of the soft carbanion onto the terminal position of the diene and subsequent PhS02- elimination to give the phenylsulfonyl sub- stituted allene. The thermal reactions of these phenylsulfonyl allenes gave (2+2)-cycloadducts. Only the Cl-C2 double bond of the alleneparticipates in the (2+2)-cycloaddition. Stepwise bonding prefers to occur in a 1 ,&ex0 manner rather than in a 1,7-endo fashion. The formation of all products can be rationalized by a mechanism which includes an initial carbon-carbon bond formation involving the central allene carbon to give a diradical intermediate. The product distribution is then determined by the substitution pattern of the alkene and the fate of the diradical intermediate.

Application of the 2,3-sigmatropic rearrangement of β-sulfonyl acetylenic carbinols toward the synthesis of 1,4-bis(phenylsulfonyl)-1,3-butadienes

Sulfenic esters of β-sulfur substituted acetylenic carbinols undergo 2,3-sigmatropic rearrangement to produce allenylic sulfoxides which were converted to 1,4-bis(phenylsulfonyl)-1,3-dienes or α,β-unsaturated ketones.

The co-oxidation of conjugated enynes. A convenient synthesis of β-sulfoxy acetylenic carbinols

Abstract Several β-sulfoxy substituted acetylenic carbinols were prepared by the addition of thiyl radicals and oxygen to conjugated enynes.