By Armin de Meijere, A. Brandi, F.M. Cordero, A. Goti, T. Hirao
This paintings on small ring compounds in natural synthesis covers cycloadditions onto methylene- and alkylidenecyclopropane, and selective ameliorations of small ring compounds in redox reactions.
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Carbon-carbon bond forming reactions are arguably crucial approaches in chemistry, as they signify key steps within the construction of complicated molecules from easy precursors. between those reactions, metal-catalyzed cross-coupling reactions are widely hired in a variety of parts of preparative natural chemistry, starting from the synthesis of advanced typical items, to supramolecular chemistry, and fabrics technological know-how.
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Additional resources for 178 Topics in Current Chemistry: Small Ring Compounds in Organic Synthesis V
The authors report about the formation of a single 5-spirocyclopropane fused regioisomer 251 (Scheme 41) . The impulse to the study of these cycloadditions came from the discovery that 5-spirocyclopropane isoxazolidines (or isoxazolines) undergo a thermal rearrangement resulting in the production of selectively substituted tetrahydro(or dihydro) pyrid-4-ones (Scheme 42) 1-64]. In particular, cyclic nitrones gave ultimately N-bridgehead bicyclic ketones, molecular skeleton of many alkaloid families .
To a minor extent, 149 also underwent a [1,3]-sigmatropic rearrangement to 151, followed by cycloaddition, to produce 152, along with [2 + 2] cycloaddition products 155 across the exocyclic double bond. The 1:2 adducts 154 and 1 : 1 adducts 155 were produced as a couple of stereoisomers. 2-Ethoxyisobutenylidenecyclopropane (150) underwent only the ene reaction followed by cycloaddition of the intermediate diene 153 (R 1 = H, R 2 = OEt, X = NPh) with 116 to give two stereoisomers of general structure 154 (R 1 = H, R 2 = OEt, X = NPh) in I:1 ratio (Table 15, entry 3).
These experimental findings, as well as earlier data on alkylidenecyclopropanes, clearly disclose a peculiar effect of a cyclopropylidene system both on reaction rates and regioselectivity. In fact, the parent MCP as well as its derivatives exhibit a high reactivity in 1,3-dipolar cycloadditions with nitrones. In contrast, the related open chain isobutene and its derivatives are well known to enter 1,3-dipolar cycloadditions sluggishly [5 lc-d, 70]. For example, there is no chance to obtain a cycloadduct from 256 and an open chain trialkyl or tetraalkylethylene, as was obtained in the reaction of 256 with 270 and 271.