Yoshinori Takanohashi

A Novel Use of Bis(2-Bromoethyl)Selenium Dibromide: Facile Formation of Tricalcogen Bonds in Metallocenophanes

Abstract 2-Selena-1,3-dicalcogena[3]metallocenophanes are obtained in high and moderate yields by the reaction of metallocene-1,1′-dithiol and -diselenol with bis(2-bromoethyl)selenium dibromide under mild conditions.

Bis(2-bromoethyl) selenium dibromide as the selenium-introducing reagent: One-pot preparation of 2,5-bis(alkoxymethyl)tetrahydroselenophenes by the cyclization of 1,5-hexadiene

Abstract The reaction of bis(2-bromoethyl)selenium dibromide (1a) with 1,5-hexadiene (2) in methanol or ethanol affords 2,5-bis(alkoxymethyl)tetrahydroselenophene-1,1-dibromides (R  CH3 (3b), R  C2H5 (3c)) via 2,5-bis(bromomethyl)tetrahydroselenophene-1,1-dibromide (3a). The reaction of 1a with 2 in 1-propanol, 2-methyl-1-propanol or 1-butanol in the presence of sodium carbonate gave 2,5-bis(alkoxymethyl)tetrahydroselenophene (R  C3H7 (4a), R  (CH3)2CHCH2 (4b) and R  C4H9 (4c)) via 3a. The ratios of the trans and cis isomers of 3a–3c are 3:2. In addition, the structure of trans-2,5-bis(methoxymethyl)tetrahydroselenophene-1,1-dibromide (trans-3b) was determined by X-ray crystallography.

Novel borane–selenium complex: highly selective reduction of tertiary amides and nitriles to the corresponding amines with sodium borohydride–dialkylselenium dibromide

The reaction of sodium borohydride with bis(2-bromoethyl)selenium dibromide and/or diethylselenium dibromide in tetrahydrofuran (THF) gave borane. Treatment of tertiary amides with mixtures of sodium borohydride and either of the dibromides in THF gave the corresponding amines. Similar reactions with secondary and primary amides did not proceed. Furthermore, under similar reduction conditions, the reaction of nitriles with the above reagents also gave the corresponding primary amines.

Reactivities of bis(2-bromoethyl)selenium dibromide and its related compounds: formation of hypervalent T-shaped coordinated selenium compounds by reaction with pyridine and its derivatives

The reaction of bis(2-bromoethyl)selenium dibromide 1 with pyridine 2a and its derivatives 2b-2d gave hypervalent T-shaped coordinated selenium compounds 3a-3d with two halogen atoms in the trans positions in moderate to good yields. Also, 2-pyridiniumethylselenol bromide 10 was obtained by the reaction of (2-bromoethyl)phenyl selenium dibromide 9 with 2a in 9.8% yield. The X-ray analysis of 10 revealed that the two conformers about the CH2-CH2 bond existed in one crystal unit, although the 1H-NMR spectra at room temperature showed relatively free rotation about the CH2-CH2 bond.

Correlation between the structure and reactivity of the selenide dihalide of the new reducing reagent NaBH4-R2SeX2 on the highly selective reduction of amides. X-ray molecular structure of bis-(2-chloroethyl)selenium dichloride

Treatment of NaBH4 with a diethylselenium dihalide generates borane which reduces amides to the corresponding amines. The reduction abilities of the reductants depend on the structure [that is, trigonal-bipyramidal (TB) or molecular complex (MC)] of 2. The order of the reduction ability is as follows: NaBH4-diiodide 2c > NaBH4–dibromide 2b > dichloride 2a. The reagents, NaBH42b and NaBH4–2a, which form TB structures can reduce the tertiary amide with high selectivity, while NaBH4–2c, which forms a molecular complex, reduces primary, secondary and tertiary amides nonselectively.

Introduction of Alkyl- or Phenylseleno Group by the Ring Opening of Cyclic Ethers Using Dialkyl- or Alkylphenylselenium Dibromide and Sodium Borohydride

Abstract The reaction of dialkyl- or alkylphenylselenium dibromide with cyclic ethers in the presence of sodium borohydride gave ω-hydroxyalkyl alkyl or phenyl selenides as the ring opening products of the cyclic ethers.

New synthesis of hypervalent T-shaped coordination compounds of selenium by the reaction of bis(2-bromoethyl)selenium dibromide with pyridine and its derivatives

The reaction of bis(2-bromoethyl)selenium dibromide 1 with pyridine 2a and its derivatives as nucleophile gave T-shaped coordination compounds of selenium 3a–3e with two halogen atoms in the trans positions in moderate to good yields. However, the reaction of bis(2-bromoethyl)selenide 4 with 2a gave 1,1′-(selanediyldiethylene) dipyridin-1-ium dibromide 5 as a normal substituted product in 42% yield. In addition, 1-(2-selanylethyl) pyridin-1-ium bromide 11 was obtained by the reaction of (2-bromoethyl)phenylselenium dibromide 10 with 2a in 29% yield. The crystal structures of 3a, 3b, 3d, 3e, 5 and 11 have been determined by X-ray analyses. The X-ray analysis of 11 revealed that two conformers about the CH2–CH2 bond exist in one crystal unit at room temperature; however, the 1H NMR spectra of the compound at room temperature showed relatively free rotation about the CH2–CH2 bond in solution.

Selenium transfer reagent: one-step alkoxyselenation of cyclohexene with bis(2-bromoethyl)selenium dibromide

The reaction of bis(2-bromoethyl) selenium dibromide 1 with cyclohexene 2 in alcohol under reduced pressure proceeds smoothly to give bis(2-alkoxycyclohexyl) selenium dibromide (R = Me 4, R = Et 5, R = Pri6)via 2-bromocyclohexyl-2′-bromoethylselenium dibromide 3 as an intermediate together with ethene. The diastereoisomers 4a and 5a (1R,2R,1′S,2′S) and 4b and 5b(1R,2R,1′R,2′R or 1S,2S,1′S,2′S) were separated from 4 and/or 5. These isomers 4a/5a and 4b/5b were isolated as a meso and a racemic mixture, respectively. Although the addition product 6a(1R,2R,1′S,2′S) was only isolated from 6 in the meso form, the corresponding diastereoisomer 6b(1R,2R,1′R,2′R or 1S,2S,1′S,2′S) was not detected. These results indicated that the Se and Br atoms in the cyclohexane ring of 3, and the Se and alkoxy groups in the cyclohexane rings of 4–6 were in the diequatorial position.