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New synthetic methods for the construction of novel heterocycles and tryptamines are described. Thus, N-Boc anilines (I) are sequentially converted to heterocycles II ((3-(2-aminophenyl)pyrrolidin-3-ol) derivatives), III (substituted 2-oxo-1,2-dihydrospirobenzo[d][1,3]oxazine-4,3'-pyrrolidines), and VI (2-(4,5-dihydro-1H-pyrrol-3-yl)aniline) derivatives through a route involving t-BuLi induced ortho-metalation/LaCl(3).2LiCl metal exchange, reaction with N-Boc pyrrolidin-3-one (5), and subsequent decarboxylative fragmentation. Labile intermediates VI are effectively converted to tryptamines Xa and Xb under controlled protic acid conditions. In addition to providing expedient access to the 2-oxo-1,2-dihydrospirobenzo[d][1,3]oxazine-4,3'-pyrrolidines (III), the method is applicable to the synthesis of the corresponding 2-oxo-1,2-dihydrospirobenzo[d][1,3]oxazine-4,3'-piperidine series of spirocycles (e.g., 42) and their precursors (3-(2-aminophenyl)piperidin-3-ol derivatives, e.g., 43) by using N-Boc-protected piperidin-3-one (40). Applications of the developed synthetic technologies to the synthesis of regioisomeric spirocycles 87 and 90, tryptamines 88 and 91, Corey's aspidophytine tryptamine (97), and efavirenz (1) are also described.

[structure: see text] This manuscript describes our synthesis of the F-H subunit of gambierol. In addition to the synthesis of the tricycle, of note is an interesting protecting group influence on the generation of a C(23) C-glycoside as well as the use of ring-closing metathesis to generate a tetrasubstituted enol ether.

This communication describes the total synthesis of the marine polyether toxin, gambierol. This work couples our iterative C-glycoside/enol ether-olefin metathesis strategy to the subunits with a unique olefin metathesis/carbonyl olefination reaction to bring the subunits together.