yl nor born ane . ▁None ▁of ▁the ▁ex o ▁di aster e omer ▁was ▁observed . ▁( 4 ) ▁En ant io select ive ▁redu ctions ▁of ▁k et ones ▁may ▁be ▁accomplished ▁through ▁the ▁use ▁of ▁catal yt ic ▁amounts ▁of ▁ch iral ▁transition ▁metal ▁complex es . ▁In ▁some ▁cases , ▁the ▁transition ▁metal ▁simply ▁serves ▁as ▁a ▁Lewis ▁acid ▁that ▁coordinates ▁to ▁the ▁k et one ▁o xygen ; ▁however , ▁some ▁met als ▁( most ▁not ably ▁co pper ) ▁react ▁with ▁hyd ros il anes ▁to ▁afford ▁metal ▁hyd ride ▁inter medi ates , ▁which ▁act ▁as ▁the ▁active ▁reducing ▁agent . ▁( 5 ) ▁In ▁the ▁presence ▁of ▁rh od ium ▁catal yst ▁ 1 ▁and ▁rh od ium ▁tr ich lor ide , ▁ 2 - phen yl cyc lo hex an one ▁is ▁reduced ▁with ▁no ▁di aster e ose lect ivity ▁but ▁high ▁en ant io select ivity . ▁( 6 ) ▁ ▁S cope ▁and ▁limitations ▁Organ os il anes ▁are ▁used ▁to ▁reduce ▁alco h ols ▁to ▁al kan es ▁in ▁the ▁presence ▁of ▁a ▁strong ▁Lewis ▁acid . ▁Br ø n sted ▁ac ids ▁may ▁also ▁be ▁used , ▁although ▁c ation ic , ▁ske let al ▁re arr ang ements , ▁and ▁nucle oph il ic ▁attack ▁of ▁the ▁conjug ate ▁base ▁on ▁the ▁car b ocation ▁may ▁be ▁problem atic . ▁The ▁rate ▁of ▁reduction ▁increases ▁with ▁increasing ▁substitution ▁at ▁the ▁alco hol ▁carbon — ter ti ary