138M.Periasamy,M.Thirumalaikumar/JournalofOrganometallicChemistry609(2000)137–151

NaBH4+CH3COOH CH3COOBH3Na 1.n-C4H9CH CH2

2.HOn-C4H9CH2CH2OH

(4)

22 OH

75%

Selectivehydroborationofole nicmoietyinthepres-enceofcarboxylicacidgroupwasreportedfromthislaboratory(Eq.(5))[9].

(5)

Also,anewmethodofconversionofole nstodialkylketonewasdeveloped(Eq.(6))[10].NaBH1.AcOH–THF

1.CHCl3–NaOMe

4 2.n-C8H17CH CH2

2.H2O2–OH 25°C,12h(n-C8H17CH2CH2)2C O

(6)

80%

Amethodofconversionofterminalalkenestocar-boxylicacidsthroughhydroborationofole nswasalsodeveloped(Eq.(7))[11].Thismethodprovidesasimple,one-potsynthesisofcarboxylicacidsfromterminalalkenes.

(7)

Also,variouscombinationsofmetalsaltsandborohy-drides,suchasSnCl4–NaBH4[12],TiCl4–NaBH4[13],TiCl4–PhCH2N+(Et)3BH 4[14]andCoCl2–NaBH4[15]havebeenreportedtoeffecthydroborationofole ns.WhereastheCoCl2–NaBH4combinationbehavesasahydroboratingagentwhenthereactioniscarriedoutwithTHFfor2hatroomtemperature(r.t.)beforetheadditionofalkene,itworksasahydrogenatingagent[15]inmethanol(Eq.(8)).Thismethodhassomeadvantagesoverthereportedmethodusingalcoholicmedium[16].

(8)

Chiralsemicorrin1–3cobaltcomplexescanbepre-paredreadilyusingCoCl2andthecorrespondingfreeligands.Thesecomplexesareef cientenantioselectivecatalystsfortheconjugatereductionofa,b-unsaturated

carboxylates(Eq.(9))[17]anda,b-unsaturatedcarbox-amides[18]usingNaBH4.

(9)

ChalconesundergofacilereductiononreactionwithNiCl2–NaBH4systemtoafforddihydrochalcones(Eq.(10))[19].TheuseofcopperorcobaltchlorideinplaceofNiCl2isnotasef cientforthisapplication.

(10)

TheNaBH4reactswithI2togivediborane(Eq.(11))[20a].

2NaBH4+I2 B2H6+H2+2NaI

(11)

Thereactive‘H3B–THF’speciescanbeeasilygeneratedinsitubymixingNaBH4andI2inTHF[20b].Hydro-borationofalkenesusingthisNaBH4–I2systeminTHFfollowedbyoxidationgivesthecorrespondinganti-Markovnikovalcohols(Eqs.(12)and(13))ingoodyields[21,22].

n-CNaBH4–I2

H2O2

8H17CH CH2 THF NaOHn-C8H17CH92%

2CH2OH

(12)

(13)

Later,itwasreportedthatelectrochemicaloxidationofNaBH4usingcatalyticamountsofsodiumiodidegivesdiboranethathydroboratesole ns(Eq.(14))[23].

(14)

TheMe3SiCl–PhCH2N+

(Et)3BH 4

reagentsystemhasbeenreportedtoeffecthydroborationofole nstogiveanti-Markovnikovalcoholsafteroxidation(Eq.(15))[24].

CH1.PhCH2N+(Et3)B H4

3(CH2)6CH CH2 Me3

SiCl,CHCl

2.H2O2 OH2

2

CH3(CH2)7CH2OH

(15)

72%