Orthocyclophanes. 1. Synthesis and characterization of [14]- and [15]orthocyclophanes and bicyclic biscyclophanes

Abstract

2-(3-Chloropropyl)-l-phenyl-2,3-butadien-l-ol (3k): yield 840 mg (93%) from Id (1.17 g, 6 mmol) and benzaldehyde (0.42 g, 4 mmol) using procedure B; purified by flash chromatography (hexane-EtOAc (98.2)); 3k:4k = 97.3; IR (neat) 3390 (br)

The First Asymmetric Halogen/Metal‐Exchange Reaction: Desymmetrization of Alcohols with Enantiotopic Bromoarene Substituents

“…Syntheses of dibromoalcohols 1 and 4: Dibromoalcohol 1 [12,13] is accessible from 2-bromobenzaldehyde in at least 40 % yield by a benzoin condensation and oxidation/benzilic acid rearrangement/decarboxylation [12] or in at least 34 % yield by the addition of 2-bromophenylmagnesium bromide. [13] We improved the yield of the latter approach to 86 % by making this Grignard reagent from 1,2-dibromobenzene (6) and iPrMgCl·LiCl (as described for a different context [8] ) rather than Mg turnings (Scheme 3).…”

“…2.5 m in hexanes) was added dropwise to an ice-cooled solution of the respective alcohol [2-(dimethylamino)ethanol or alcohols [11][12][13][14][15][16][17][18][19][20] in THF (0.2-1 m). After 30 min, the cooling bath was removed and stirring continued for another 30 min.…”

The McMurry Coupling and Related Reactions

“…These reactions, which were shown to involve zinc carbenoid intermediates resulting from reduction and deoxygenation of ketyl radicals, also produce a number of side products, in particular pinacols and coupled alkenes, which are the normal products of McMurry reactions; it has been demonstrated that the deoxygenative coupling process does not proceed via pinacol-type intermediates. It is very interesting to note that the same orthocyclophane 87 was obtained in 91% yield by treating its dicarbonyl precursor with Zn(Hg) and HCl in place of the TiCl 3 -LiAlH 4 system [121]. Moreover, the chlorosilane-modified Clemmensen reduction has, in some cases, proved to be a useful alternative to the McMurry alkene synthesis, in particular with electron-rich aromatic carbonyl compounds and metallocenic ketones [297].…”

“…In many cases, as for 85 [114] and 86 [115], these compounds are formed together with the products resulting from successive inter-and intracyclization reactions (Section 6.2.3) [114][115][116][117][118][119]. Transannular coupling reactions have allowed access to the higher orthocyclophane derivative 87 [120,121], the triply-bridged cyclophane 88 [122], as well as the highly distorted cone calix [4] arenes derivatives, including 97, was synthesized for a study of their photoswitchable properties; the coupling reactions yielded both cis-and trans-stilbenes from o-and m-bis(benzaldehyde)s, while only the cis-stilbene was obtained from the p-isomer [133]. Polyepoxyannulenes such as 98 were found to be highly dynamic systems [134][135][136].…”

Polymethylhydrosiloxane reduction of carbonyl function catalysed by titanium tetrachloride

“…However, the drastic reaction conditions of both processes have given rise to various other methods, all in an effort to find milder reaction conditions. Some of the alternative methods include catalytic hydrogenation [4][5], reductions using Raney nickel in hydroxide media [6], reductions using PtO 2 [7], HI-phosphorus [8][9], NaBH 4 -CF 3 COOH [10][11], NaCNBH 3 -BF 3 Et 2 O [12], LAH-AlCl 3 [13]. While these methods offer some advantages, they also suffer from some disadvantages.…”