复旦大学：《有机化学A》课程教学资源（学生课件）a,b-不饱和醛酮的还原 Reduction of a,b - unsaturated carbonyl compounds

Reduction of a,- unsaturated carbonyl compounds Edited by Chen Peng, Gao Dong

Reduction of a,b - unsaturated carbonyl compounds Edited by Chen Peng , Gao Dong

Part one Chemoselective Reductions or not?

Part one Chemoselective Reductions or not?[1]

By Nabh4 or LiAlH4 A is obtained orb ??? O OH HO C=c—C C=c—C +H—C—C—C H H B

By NaBH4 or LiAlH4 A is obtained or B ??? C C C O C C C O H H C C C HO H H H + A B

Substrate Yield.NaBHa, 50% aqueous EtoH- LiAlH, ether- %o A 7 B Yield, %o 7A %O B CH,-CHCCH( CHCH=CHOCH,(2) 65 35 98 (CHA)C=CHOCH(3) 92 59 97 100 CH, "CHCH (6) CHCHe CHCH (7) 92 94 100 CH=C-cH⑧ ≥99 ≤1 98 ≥99 ≤1 CHO

Other way to illustrate CH3 O (CH3)2C-CHCCH3 2HC-C-CH2 CHCH2 OH OH C OH (CH3)2C-CHCHCH2 (CH3)2CHCHCHCH2 H2C=CCH2 CHCH2 22 23 Starting - meteria 一 Product distribution %6 3 21 Reduction conditions %o12 22 %23 97 3 LiAlH, ether 60 40 LiAIH, ether 040 97 3 NaBH4, 50%o aq ethanol 97 3 NaBH, 507 aq methanol 87 10 3 60 40 NABH, i-PrOH 561725 97 3 NaBH, i-PrOH 542817

H2C C CH3 CH2CHCH2 OH CHCH2 OH (CH3)2C CH CHCH2 OH (CH3)2CHCH2 + + CHCCH3 O (CH3)2C 2HC C CH3 CH2CHCH2 O + 3 21 12 22 23 Other way to illustrate

attention the effect NaBH4 of solution!! I-ProH H A B

attention the effect of solution!! O NaBH4 i-PrOH O C + O H O B + H H H H O A H H

TABLE II REDUCTION BY SODIUM BOROHYDRIDE IN ISOPROPYL ALCOHOL Produet distribution Substr我te Yield,%% A %o B 7 C 10 60 34 83 65 34 25 48 63 37 0 69 53 26 21 26 8 ≥95 ≤4 Substrates 1to 9 refer to page 4

Substrates1to 9 refer to page 4

Summery: NaBH4 reduction with i-PrOH fast i-PrOh c=c-c—OBoR)4 c=c-c—0H+B(oi-Pr)4 BH H OH BH i-PrOh C=C-C c一c=c-0B(OR)4 c-c—c 19 i-PrOE i-PrO C-C-C BH4,c一

Summery:NaBH4 reduction with i-PrOH C C C O C C C OB(OR)4 - H C C C OH H + B - (Oi -Pr)4 fast i -PrOH BH4 - C C C OB(OR)4 - H C C C O 19 19 C C C OH i -PrOH + BH4 - H C C C O O C C C OH O H + 19 BH4 - 20 i -PrOH i -PrO - BH4 -

Summery of part one Both nabh4 and lialh4 have been observed to give both types of product, although the extent of reduction to saturated alcohol is usually greater with NaBH4 Solution can lead to other product See part two to further research

Summery of part one • Both NaBH4 and LiAlH4 have been observed to give both types of product , although the extent of reduction to saturated alcohol is usually greater with NaBH4 • Solution can lead to other product See part two to further research

Part two Several reagents have been developed which lead to exclusive 1.2- or 1 4-reduction

Part two Several reagents have been developed which lead to exclusive 1,2- or 1,4-reduction