Cyclocondensation reaction of a 1,5-diketone with 1,2-diamines

Reaction of 2-acetonyl-4,5-dimethoxy-3′-chlorobenzophenone (1) with ethylenediamine afforded the imidazo[2,1-a]isoquinoline 2, whereas 6-(3-chlorophenyl)-8,9-dimethoxybenzo[b]phenazine (3) and naphthol 4 were obtained with ortho-phenylenediamine.     

Free radical ring expansion and spirocyclization of 1,3-diketone derivatives

Free radical-promoted three-carbon ring expansions of 1,3-diketones to form corresponding nine-membered 1,6-diketones and associated spirocyclization reactions are described.     

Opening of tartrate acetals using dialkylboron bromide: evidence for stereoselectivity downstream from ring fission

Johnson-type acetals derived from dimethyl tartrate give, after opening with Me(2)BBr and cuprate displacement, secondary alcohols with high diastereoselectivity (>30:1). The mechanism proposed for the induction of diastereoselectivity is downstream from the ring fission. It implies a direct participation of the Lewis acid as a source of nucleophile and the stereospecific transformation of the resulting bromo acetal through an invertive and temperature-dependent process. The acetals are prepared by reaction of the desired aldehyde with dimethyl tartrate. Removal of the auxiliary is accomplished through SmI(2) reduction or by an addition-elimination protocol using methoxide.     

Divergent stereoselectivity in the photoaddition of alkanals and medium ring cycloalkenes

Photocycloaddition of alkanals and cycloheptene, cyclooctene, and 1,5-cyclooctadiene results in stereoisomeric oxetanes, the composition of which depends on the concentration of starting alkene.     

Triphenylphosphine-induced ring contraction of 1,2-dioxines

Triphenylphosphine inserts into the peroxide bond of 1,2-dioxines, initiating ring contraction with loss of triphenylphosphine oxide. This process yields dihydrofuran oxides in 54-97% yield from oxirenyl[2,3-c][1,2]dioxines and dihydrofurans from 3,6-dihydro-1,2-dioxines with inversion of stereochemistry at either the 2 or 5 position in the furan product.     

Stereospecific [1,2]-rearrangement of a spirocyclic ammonium ylide with ring expansion sequence

Enantiomerically pure bicyclic 1,4-oxazepinone was obtained by the Cu(II)-catalyzed decomposition of an α-diazo carbonyl compound tethered to a chiral morpholinone, through the cascade evolution of the spirocyclic ammonium ylide formed. LiAlH₄ reduction and transesterification of the lactone moiety of the oxazepinone afforded pure chiral pyrrolidine and 3-prolinone bicyclic hemiacetal, respectively, both bearing a quaternary stereocentre.     

Silylcuprates from allene and their reaction with alpha,beta-unsaturatedd nitriles and imines. Synthesis of silylated oxo compounds leading to cyclopentane and cycloheptane ring formation

The silylcupration of allenes and the subsequent capture of the intermediate cuprate with alpha,beta-unsaturated nitriles is reported. The influence of the substitution of the nitrile, the nature of the silylcopper species, and the temperature on the selectivity of the reaction is studied. An interesting diaddition process was observed (1,2-addition and 1,4-addition), leading to oxo compounds which simultaneously have an allylsilane and a vinylsilane group. The different reactivity of these two units has been employed in the intramolecular allylsilane-terminated cyclization of these adducts, where the vinylsilane moiety remains unchanged. To shed some light on the reaction pathway, the behavior of alpha,beta-unsaturatedd imines was also checked and a new and convenient way for cycloheptane annulation presented. In light of the former results a feasible mechanism is proposed.     

Synthesis and properties of a bridged nucleic acid with a perhydro-1,2-oxazin-3-one ring

A novel derivative of 2',4'-bridged nucleic acid, named hydroxamate-bridged nucleic acid (HxNA), containing a six-membered perhydro-1,2-oxazin-3-one ring, was designed and synthesized. The introduction of a carbonyl function along with an N-O linkage in the six-membered bridged structure is the unique structural feature of the novel 2',4'-bridged nucleic acid analogue. The design was carried out to restrict the flexibility of the sugar moiety through the trigonal planarity of carbonyl function, which would improve the properties of the modification. The synthesized monomer was incorporated into oligonucleotides, and their properties were examined. The HxNA-modified oligonucleotides exhibited selectively high affinity toward complementary ssRNA. Furthermore, the nuclease resistance of the HxNA-modified oligonucleotide was found to be higher than that of the corresponding natural and 2',4'-BNA/LNA-modified oligonucleotides. Interestingly, exposure of HxNA modified oligonucleotide to 3'-exonuclease resulted in gradual opening of the bridge, which stopped further digestion. Moreover, ring-opening of only one modification at the 3'-end of the oligonucleotides was observed, even if two or three HxNA modifications were present in the sequence. The results demonstrate the strong potential of the HxNA modification as a switch for the generation of highly nuclease-resistant RNA selective oligonucleotide in situ, which could have potential applications in antisense technology.     

Preparation of derivatives of 1,2-dihydro- and 1,2,3,6-tetrahydropyrazinones from acylated 1,2-hydroxylamino ketones

N-(2-Oxoalkyl)-2-chloroacetohydroxamic acids were obtained by acylation of 1,2-hydroxylamino ketones with chloroacetyl chloride. Their reaction with urotropin and sodium azide gives urotropinium salts and acetoxyhydroxamic acid azides. 1-Hydroxy-2-oxo-1,2,3,6-tetrahydropyrazines were obtained by treating N-(2-oxoalkyl)-2-chloroacetohydroxyamic acids with ammonia, and also by reacting the urotropinium salts and azides of acetohydroxamic acids with hydrochloric acid and triphenylphosphine, respectively. The reaction of N-(1-methyl-2-oxo-2-phenylethyl)-2-chloroacetohydroxamic acid with urotropin in an acid medium leads to the formation of 6-methyl-2-oxo-5-phenyl-1,2-dihydropyrazine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 509–513, April, 1986.     

Unusual mixed valent FeIIIFeII complex (St = 3/2) stabilised by a reduced bulky 1,2-diketone

The reduction of the bulky 1,2-diketone bis(2,6-diisopropylphenyl)glyoxal () and FeBr(2) with 1.5 equivalents of Na results in a Class 2 mixed valent H.S. Fe(II) L.S. Fe(III) complex (2) with two five-coordinate Fe centres which are antiferromagnetically exchange-coupled to give a total spin S(t) = 3/2 ground state and an S(t) = 5/2 excited state that are separated by about 25 cm(-1) (for Delta(J) approximately 5J).     

Alkenylimmonium salts as dienophiles in Diels-Alder cycloadditions with high reactivity and stereoselectivity

Alkenylimmonium salts, such as the substituted vinylpyridinium salts, 6, 7, 12, and 16, are easily prepared and are very reactive dienophiles in Diels-Alder cycloadditions.     

Note on the Preparation of 1,2-Diketones from Acetylenes

A mild method for the oxidation of acetylenes to 1,2-diketones using NaIO₄/RuO₂ is described. An investigation on the compatibility of various functional groups with this oxidizing agent is reported.