ann ane ▁to ▁a cy l ▁ch lor ides . ▁However , ▁these ▁mo iet ies ▁are ▁not ▁always ▁readily ▁available ▁and ▁can ▁be ▁difficult ▁to ▁form , ▁especially ▁in ▁the ▁presence ▁of ▁sensitive ▁functional ▁groups . ▁Furthermore , ▁cont rolling ▁their ▁high ▁react ivity ▁can ▁be ▁challeng ing . ▁ ▁The ▁St ille - car b ony l ative ▁cross - cou pling ▁emp lo ys ▁the ▁same ▁conditions ▁as ▁the ▁St ille ▁coupling , ▁except ▁with ▁an ▁atmosphere ▁of ▁carbon ▁mon ox ide ▁( CO ) ▁being ▁used . ▁ ▁The ▁CO ▁can ▁coordinate ▁to ▁the ▁p all ad ium ▁catal yst ▁( 9 ) ▁after ▁initial ▁ox id ative ▁addition , ▁followed ▁by ▁CO ▁insert ion ▁into ▁the ▁P d - R 1 ▁bond ▁( 1 0 ), ▁resulting ▁in ▁subsequent ▁re duct ive ▁elim ination ▁to ▁the ▁k et one ▁( 1 2 ). ▁ ▁The ▁trans met al ation ▁step ▁is ▁normally ▁the ▁rate - det erm ining ▁step . ▁ ▁Larry ▁Over man ▁and ▁cow ork ers ▁make ▁use ▁of ▁the ▁St ille - car b ony l ative ▁cross - cou pling ▁in ▁their ▁ 2 0 - step ▁en ant io select ive ▁total ▁synth esis ▁of ▁st ry chn ine . ▁ ▁The ▁added ▁car b ony l ▁is ▁later ▁converted ▁to ▁a ▁terminal ▁alk ene ▁via ▁a ▁W itt ig ▁reaction , ▁allowing ▁for ▁the ▁key ▁t ert i ary ▁nit ro gen ▁and ▁the ▁pent acy clic ▁core ▁to ▁be ▁formed ▁via