Mechanism B: Acid catalyzed Acid: H2 SO4 Hcl, TsOH, etc. R-CH2-C-R.H+ R—CH2-C—R R—CH2—C-R O OH HO RR O 2 R一CH3-C—R+R—HC=C—R=~R-C-C-C—C—R HO OH OH R H2O R R-C—C RICH C—R C=C-CR ④OH2 RH2C RAcid: H2SO4, HCl, TsOH, etc. Mechanism B：Acid catalyzed R H2 C C C H C R ' R ' R OH2 O C C CR' R H - H2 O -H O R' RH2 C R CH2 C R' O R CH2 C R' OH R CH2 C R' HO H + R HC C R' OH R CH3 C R' HO R H2 C C C H C R ' R ' R OH O +