Marine alkaloids synthesis stereochemistry

Perhydropyrido[l,2-A][l,2]oxazines have been utilized as key intermediates in a stereospecific total syntheses of (—)-pumiliotoxin C and 5-< />z-pumiliotoxin C <1996J(P1)1113>, and the marine alkaloids (—)-lepadins A, B, and C and macrocyclic dilactones, (+)-azimine and (+)carpaine <20000L2955, 2001JOC3338, 2003OL3839>. In the total synthesis of the marine alkaloids ( )-fasicularin and ( )-lepadiformine, perhydro[l,2]oxazino[3,2 /]quinolines were used to control the stereochemistry <2000JA4583, 2000TL1205>. 

Total synthesis of (—)-nakadomarin A 31, a marine alkaloid of the manzamine family, " was reported by Dixon and co-workers In their synthesis, a bifunctional organocatalyst derived from cinchonidine was effective for the Michael addition reaction of 27 and 28, and stereochemistries at C7 and C8 were efficiently controlled. In this reaction, low selectivity or decomposition of the nitroolefin was observed with the stoichiometric use of lithium 1,1,1,3,3,3-hexamethyIdisiIazide, (or lithium bis(trime-thylsilyl)amide) (LHMDS), potassium 1,1,1,3,3,3-hexam-ethyldisilazide [potassium bis(trimethylsilyl)amide] (KHMDS), or I,4-diazabicycIo[2.2.2]octane (DABCO) (Scheme 27.5). 

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