Organo-SOMO catalysis polycyclizations

Metabolic cyclization routes of polyenes leading to terpenes [1] inspired chemists to synthesize steroids and polycyclic structures [2]. Metal catalysis, chiral auxiliaries, substrate control, and other stoichiometric methods reach some level of success [3], but only recently Rendler and MacMillan published independently two approaches using organo-SOMO catalysis to synthesize these features (Scheme 10.1) [4], as a continuation of their work on the asymmetric cyclization of aldehydes [5]. 

SCHEME 10.2. Organo-SOMO catalysis mechanism for polycyclization. 

Organo-SOMO catalysis was also applied to polyene cyclization. In 2010, MacMillan reported an enantioselective cyclization reaction of substrates 41 for accessing steroidal and terpenoidal frameworks. They used imidazolidinone 40 instead of catalyst 23, with the aid of copper(ll) triflate as the oxidant. The polyene cyclization took place smoothly, giving polycyclic systems 42 and even more complex compounds 43 or 44 in good yields and with high enantioselectivity and exclusive diastereoselectivity (Scheme 36.12) [18]. 

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See also in sourсe #XX -- [ , , ]

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