▁(+ )- estr one ▁re lies ▁on ▁select ive ▁hyd ros il ane ▁reduction ▁of ▁a ▁conjug ated ▁alk ene ▁as ▁a ▁key ▁step . ▁The ▁k et one ▁car b ony l ▁and ▁isolated ▁double ▁bond ▁are ▁una ffect ed ▁under ▁the ▁conditions ▁shown . ▁( 1 5 ) ▁ ▁Com parison ▁with ▁other ▁methods ▁A ▁variety ▁of ▁alternative ▁methods ▁for ▁the ▁en ant io select ive ▁reduction ▁of ▁double ▁b onds ▁are ▁known . ▁Most ▁of ▁these ▁employ ▁catal yt ic ▁amounts ▁of ▁a ▁transition ▁metal ▁complex ▁and ▁use ▁hydro gen ▁gas ▁as ▁the ▁reducing ▁agent . ▁For ▁instance , ▁ir id ium ▁complex es ▁of ▁ch iral ▁ph osph ine - ox az oline ▁lig ands ▁catal y ze ▁the ▁hydro gen ation ▁of ▁tr is ub st it uted ▁al ken es ▁in ▁high ▁yield ▁and ▁en ant io se le cit ivity . ▁( 1 6 ) ▁K et ones ▁may ▁be ▁reduced ▁using ▁either ▁transfer ▁hydro gen ative ▁methods . ▁or ▁with ▁hydro gen ▁in ▁the ▁presence ▁of ▁rh od ium ▁catal yst s . ▁The ▁example ▁below ▁uses ▁the ▁P enn Ph os ▁lig and . ▁( 1 7 ) ▁ ▁Typ ical ▁Cond itions ▁Str ong ▁ac ids , ▁such ▁as ▁trif lu oro ac etic ▁acid , ▁are ▁often ▁used ▁in ▁hyd ros il ane ▁redu ctions ▁and ▁should ▁be ▁handled ▁with ▁extreme ▁care . ▁H yd ros il anes ▁under go ▁hydro ly s is ▁in ▁strong ▁acid ▁or ▁base ▁( aff ording