Ring Formation through Intramolecular SN' Displacement of an Allylic Methoxy Substituent

Formalizing the mechanism of the allylic substitution reaction (SN’): application to the highly enantio- and diastereo-selective syntheses of 1-phenyl-2-vinyl-cyclopentanes

“…13 The intramolecular version the SCN', 18 to which this work belongs, offers the advantage to avoid competing direct substitution reactions (SN) that are usually observed. It leads to cyclic compounds, including alkenyl substituted five-membered heterocycles (Scheme 11) 11,17 and carbocycles (Scheme 12, 13) 6,18,[38][39][40] whose stereochemistry at the carbon on the cycle bearing the alkenyl group as well as of CC double bond offer precious indications about the mechanism of the reaction.…”

“…16,17 Most of the reactions so far described did indeed involve the syn-mode 5-10 and generate compounds bearing usually E-CC double bonds, [5][6][7][8][9][10] unless it is part of a medium ring. Although products possessing the Zstereochemistry have been from time to time described, often as side products, 6,12,16,17,38 they usually proceed through the syn-mode.…”

“…Those, inter alia, involve: (i) the nature of the leaving group, (ii) the stereochemistry of the CC double bond, (iii) the nature, hardness of the nucleophilic atom, and nature of the counter ion for charged nucleophiles, (iv) the nature of the solvent and conformational bias resulting from the presence of the CC double bond in a cycle [5][6][7][8][9] either on the starting material or on the product and last but not least steric effects. 2,[4][5][6][7][8][9][10][11][12][14][15][16][17][18][37][38][39][40][41][42] We have gathered in Schemes 11-16 some typical reactions, that have appeared in the literature over the last 40 years. [5][6][7][8][9] They all involve as starting materials unsaturated straight-chain organometallics that produce five-membered rings 6,11,17,18,[38][39][40] via intramolecular allylic substitution reactions leading to the departure of a benzoate (Scheme 11, 11 Scheme 12, 17 Scheme 14 18 ) or an alkoxide located on the allylic site (Scheme 13, 38 Scheme 15, 39 Scheme 16 6 ).…”

“…2,[4][5][6][7][8][9][10][11][12][14][15][16][17][18][37][38][39][40][41][42] We have gathered in Schemes 11-16 some typical reactions, that have appeared in the literature over the last 40 years. [5][6][7][8][9] They all involve as starting materials unsaturated straight-chain organometallics that produce five-membered rings 6,11,17,18,[38][39][40] via intramolecular allylic substitution reactions leading to the departure of a benzoate (Scheme 11, 11 Scheme 12, 17 Scheme 14 18 ) or an alkoxide located on the allylic site (Scheme 13, 38 Scheme 15, 39 Scheme 16 6 ).…”

“…As general trends, the reactions reported in Schemes 11-16 produce compounds in which the fivemembered ring 6,11,17,18,38,39 is substituted by a E-CC double bond and only rarely by a Z-CC double bond (Scheme 12, 7 Scheme 13, 38 Scheme 16, entry b 6 ).…”