Total synthesis of (+)-grandiamide D, dasyclamide and gigantamide A from a Baylis–Hillman adduct: A unified biomimetic approach

• Andivelu Ilangovan and
• Shanmugasundar Saravanakumar

Beilstein J. Org. Chem. 2014, 10, 127–133, doi:10.3762/bjoc.10.9

• start with the same for the synthesis of dasyclamide (6). As explained in Scheme 5 attempts to get enamide 22 by reductive dehydroxylation of compound (±)-18 using NaBH4/CuCl2·2H2O or Al-NiCl2·2H2O [16][17][18] and reductive deacetoxylation of compound (±)-21 using NaBH4/t-BuOH or LiBEt3H, THF [19][20

Towards stereochemical control: A short formal enantioselective total synthesis of pumiliotoxins 251D and 237A

• Jie Zhang,
• Hong-Kui Zhang and
• Pei-Qiang Huang

Beilstein J. Org. Chem. 2013, 9, 2358–2366, doi:10.3762/bjoc.9.271

• consisting of ozonolysis and reductive dehydroxylation provided the indolizidine derivative 5, which completed the formal enantioselective total synthesis of pumiliotoxins 251D and 237A. Keywords: enantioselective synthesis; Grignard reagent; pumiliotoxin 237A; pumiliotoxin 251D; reductive dehydroxylation

• 3 h, which gave regioselective carbinol 15 as a mixture of two diastereomers. Without separation, the mixture was treated with Et3SiH/BF3·Et2O (−78 °C to rt, 2 h) [32] to yield the reductive dehydroxylation products 16 and 17 in a ratio of 98:2 (determined by 1H NMR) [32] (combined yield: 88% over 2

• form the indolizidinone ring. Thus, ozonolysis of olefin 22 in dichloromethane [51], followed by quenching with Me2S furnished the hemiaminal tautomer via intermediacy of lactam-aldehyde. Without isolation, the crude was subjected to the reductive dehydroxylation with Et3SiH/BF3·Et2O (CH2Cl2, −78 °C

A divergent asymmetric approach to aza-spiropyran derivative and (1S,8aR)-1-hydroxyindolizidine

• Jian-Feng Zheng,
• Wen Chen,
• Su-Yu Huang,
• Jian-Liang Ye and
• Pei-Qiang Huang

Beilstein J. Org. Chem. 2007, 3, No. 41, doi:10.1186/1860-5397-3-41

• more conveniently, N,O-acetal 5a, was converted to lactam 6a under standard reductive dehydroxylation conditions in 78% or 77% yield. Reduction of lactam 6a with borane-dimethylsulfide provided pyrrolidine 8 in 95% yield. Compound 8 was then converted to 1-hydroxyindolizidine ent-3 via a four-step

• to N,O-dibenzyl malimide (4) leads to N,O-acetals 5 in high regioselectivity (Scheme 2), and the subsequent reductive dehydroxylation gives 6 in high trans-diastereoselectivity.[35] On the other hand, treatment of N,O-acteals 5 with an acid furnished enamides E, which can be transformed

• equally surprising is that no dehydration product was observed under acidic conditions! For the synthesis of ent-3, aza-spiropyran 7, a cyclic N,O-acetal, was converted to lactam 6a under standard reductive dehydroxylation conditions (Et3SiH, BF3·OEt2, −78°C, 6 h; warm-up, yield: 78%) (Scheme 4). Under