Elimination

Elimination to alkyne: 2,3-dibromopropionaldehyde diethyl acetal (a vicinal dihalide) with KOH; H2O, pentane gives 3,3-diethoxypropyne (the terminal alkyne).

Leaving group elimination: 2-bromo-1,1-diethoxyethane (a primary alkyl bromide) with tBuOK, Δ gives 1,1-diethoxyethene (the enol ether).

Dehydration of alcohol: 1-vinylcyclohexyl alcohol (an allylic alcohol) with TsOH; Hexane gives vinylcyclohexene (the cyclic conjugated diene). 81% yield.

Hofmann elimination: N,N-dimethylcyclooctanamine (a tertiary amine) with 1) CH3I, CH3OH; 2) Ag2O, H2O; 3) vacuum, Δ gives cyclooctene (the eight-membered cycloalkene).

Aryne formation: a Grignard reagent gives benzyne.

Cope elimination: N,N-dimethylcyclohexanemethanamine (a tertiary amine) with 1) H2O2, CH3OH; 2) 160 °C gives methylenecyclohexane (the 1,1-disubstituted alkene).

Decarboxylative elimination: a vicinal dihalide with 1) 1 equiv. Et3N; 2) 1 equiv. DBU gives phenylacetylene (the terminal alkyne).

Oxime dehydration to nitrile: an oxime gives 5-(2,5-dimethylphenyl)-1,2-oxazole-3-carbonitrile.

Retro-oxa-Michael: a cyclic ether with TsOH; PhH gives the α,β-unsaturated ketone. 69% yield.

Elimination to alkyne: 2,3-dibromosuccinic acid (a vicinal dihalide) with 1) KOH; 2) H2SO4 (excess) gives 2-butynedioic acid (the internal alkyne).

Leaving group elimination: 3-chloro-1,1-diethoxypropane (a primary alkyl chloride) with KOH gives 3,3-diethoxy-1-propene (the terminal alkene).

Dehydration of alcohol: 2-bromo-1-indanol (a halohydrin) with TsOH; PhMe gives 2-bromo-1H-indene (the trisubstituted five-membered cycloalkene).

Elimination to alkyne: 10,11-dibromoundecanoic acid (a vicinal dihalide) with 1) NaNH2 (3 equiv), Δ; 2) H3O+ (HCl, H2O) gives 10-undecynoic acid (the terminal alkyne).

Elimination to alkyne: (1,2-dibromo-2-phenylethyl)benzene (a vicinal dihalide) with KOH, CH3CH2OH; Δ gives diphenylacetylene (the internal alkyne).

Elimination to alkyne: a vicinal dihalide with Chin. J. Chem. 2011, 29, 2350; K2CO3; DMSO; 12 hr 115 ºC gives phenylacetylene (the terminal alkyne).

Leaving group elimination: a cyclic ether with 1) DBU; 2) HCl workup gives the six-membered cycloalkene. 80% yield.

Leaving group elimination: 2-cyano-1,3-diphenylpropan-2-yl methanesulfonate (a tertiary sulfonate ester) with DBU; MeCN gives (E)-2-benzyl-3-phenylprop-2-enenitrile (the trisubstituted alkene).

Dehydration of alcohol: a secondary alcohol with MsCl / Et3N; CH2Cl2 gives the six-membered cycloalkene.

Elimination to alkyne: ethyl 2,3-dibromo-3-phenylpropanoate (a vicinal dihalide) with KOH; CH3CH2OH, Δ gives potassium 3-phenylpropiolate (the internal alkyne).

Leaving group elimination: a secondary alkyl bromide with tBuOK; THF gives the five-membered cycloalkene. 88% yield.

Leaving group elimination: a cyclic ether with H2SO4; H2O THF gives the tetrasubstituted six-membered cycloalkene. 99% yield.

Hofmann elimination: a tertiary amine with 1); 2) gives the trisubstituted six-membered cycloalkene. 84% yield.

Leaving group elimination: a cyclic ether with hindered base; LiHMDS; then H3O+ workup gives the trisubstituted six-membered cycloalkene. 80% yield.

Dehydration of alcohol: a tertiary alcohol with 1) TsOH / Me2CO; 2) Na2CO3 / H2O; workup gives 3,4,5,6,7,8-hexahydro-1(2H)-naphthalenone (the tetrasubstituted six-membered cycloalkene). 90% yield.

Leaving group elimination: a vicinal dihalide with KOH; MeOH gives 1,2-dibromocyclohex-1-ene (the tetrasubstituted six-membered cycloalkene). 71% yield.

Elimination to alkyne: 9,10-dibromo-stearic acid (a vicinal dihalide) with Na (3 equiv.); NH3 gives sodium stearolate (the internal alkyne).

Dehydration of alcohol: cyclohexanol (a secondary alcohol) with H2SO4, Δ gives cyclohexene (the six-membered cycloalkene).

Dehydration of alcohol: 2-pentanol (a secondary alcohol) with H2SO4; Δ gives trans-2-pentene (the trans-1,2-disubstituted alkene).

Elimination to alkyne: (1,2-dibromoethyl)benzene (a vicinal dihalide) with Na, NH3 gives phenylacetylene (the terminal alkyne).

Elimination to alkyne: (2Z)-1,3-dichloro-2-butene (a vinyl chloride) with KOH, 170 °C; ethylene glycol, n-butyl Cellosolve gives vinyl acetylene (the terminal alkyne).

Dehydration of alcohol: 3-chloro-alpha-methylbenzenemethanol (a benzylic alcohol) with KHSO4; Δ gives m-chlorostyrene (the terminal alkene).

Elimination to alkyne: trans-beta-bromostyrene (a vinyl bromide) with KOH; 200 °C gives phenylacetylene (the terminal alkyne).

Leaving group elimination: 2-bromo-2-methyldodecanoyl bromide (a vicinal dihalide) with KOtBu; tBuOH, Δ gives tert-butyl 2-decylacrylate (the 1,1-disubstituted alkene).

Leaving group elimination: 1,2-dibromocyclohexane (a vicinal dihalide) with i-PrOH, NaH, 100-110 °C; triethylene glycol dimethyl ether gives 1,3-cyclohexadiene (the cyclic conjugated diene).

Leaving group elimination: 7-chloro-7-methyldispiro[2.0.24.13]heptane (a tertiary alkyl chloride) with KOtBu gives 7-methylidenedispiro[2.0.2~4~.1~3~]heptane (the 1,1-disubstituted alkene).

Elimination to alkyne: 3-cyclohexyl-2-bromopropene (a vinyl bromide) with NaNH2, Δ; mineral oil gives (prop-2-yn-1-yl)cyclohexane (the terminal alkyne).