Rearrangement of isoxazoline-5-spiro derivatives. 5. Diastereofacial selectivity in the cycloaddition of substituted five-membered cyclic nitrones and methylenecyclopropanes. Stereoselective synthesis of 3,5-substituted indolizidinones
One-Pot Preparation of Quinolizidin-2-one and Indolizidin-7-one Ring Systems. Concise Total Syntheses of (.+-.)-Myrtine, (.+-.)-Lasubine II, and (-)-Indolizidine 223AB
摘要:
highly efficient approach to the quinolizidine alkaloids (+/-)-myrtine (4) and (+/-)-lasubine II (5) and to the indolizidine alkaloid (-)-indolizidine 223AB (6) is described. The preparation of quinolizidin-2-ones 4/4a and 11b/12b and indolizidin-7-ones 16/17 is based on the addition of 2-((trimethylsilyl)oxy) 1,3-dienes 2a,b and 2c to cyclic N-acyliminium ions 10 and 15, respectively. It encompasses five chemical transformations in the same pot yielding the axially oriented substituent at C-4 and C-5 as the major product in the quinolizidin-2-one and indolizidin-7-one systems, respectively. The thermodynamically more stable isomers 12b and 17 were obtained after basic treatment.