a Convenient Procedures for Birch reduction

Turk J Chem
29 (2005) , 513 - 518.
http://journals.tubitak.gov.tr/chem/issues/kim-05-29-5/kim-29-5-7-0504-3.pdf

The reduction of aromatic rings by solutions of alkali metals in liquid ammonia was discovered by Wooster and Godfrey14, who reacted toluene with sodium in ammonia followed by the addition of water. They reported a "highly unsaturated liquid product", which was not identied further. However, the real development of this reaction was to follow in the work by Birch15. This reaction is generally referred to as the Birch reduction, although in some cases it is simply called metal-ammonia reduction. Wild and Nelson16 found adding alcohol last to be advantageous, as opposed to having it present when the metal is added, and it was subsequently discovered that it should be avoided altogether with polynuclear compounds.

Compared to the other reduction procedures of converting benzene and its derivatives to corresponding nonconjugated dienes, the new reduction procedures have certain advantages. These include the following:
1) These reduction reactions are carried out at room temperature, avoiding the low temperatures, under -33oC, needed to obtain liquid NH3.
2) The procedures are environmentally friendly30−34. Much more NH3 is needed when liquid NH3 is used as solvent. Evaporation of liquid NH3 may damage the environment.
3) Control of moisture is easier in our method, and the reaction may go on for longer periods. When the reaction is conducted with liquid ammonia, it may be quenched by the developing moisture.
4) Evaporation of liquid NH3 may take a long time and some side reactions such as isomerization and reoxidation may be observed. \
5) It is unnecessary for the researcher to observe the reaction carefully and continuously in the
present method because temperature control is not necessary, whereas the temperature must be checked in the reaction with liquid NH3.

Procedure 1: Reduction of benzene to 1,4-cyclohexadine.
In a 500-mL, 2-necked, round-bottomed flask tted with a reflux condenser and a stirring bar were placed tert-butanol (72 g, 0.963 mol, 2.85 equivalents), dry benzene (27.3 g, 0.35 mol, 1 equivalent) and dry THF (120 mL). The flask was attached to gas ammonia (NH3) whose pressure was approximately 1 atmosphere (atm) and the resulting solution was stirred. The reaction mixture was cooled in an icewater bath and then freshly cut lithium (7.35 g, 1.05 g-atom, 3 equivalents) was added over 3-5 min. The temperature of the bath was allowed to rise gradually to room temperature. After the addition of lithium was completed, the reaction mixture was stirred for 5 h. Two phases appeared in the reaction mixture.
The top and bottom phases were brown and gray, respectively. The mixture was cooled in an ice-water bath again. Cold water was added slowly and carefully to the flask until all the lithium was consumed, as evidenced by the conversion of the colors to white. The reaction mixture was poured into a mixture (250 g) of water and ice and was acidied with the addition of 2 N cold hydrochloric acid. The organic layer was separated and washed with cold water (100 mL), a solution of NaHCO3 (5%, 50 mL) and water (75 mL), in order that. The reduction product, 1,4-cyclohexadiene, was dried over CaCl2 and ltered. The yield (23.5 g) and conversion of the reaction were 84% and 100%, respectively.

Note:
checked this reaction by myself, it really works.

substrates scope:
obviously, product of entry 5 and 6 should be switched.

All-Up Reactive Conformation of Chiral Rhodium(II) Carboxylate Catalysts

by
Vincent N. G. Lindsay, Wei Lin, and Andre´ B. Charette*
doi: 10.1021/ja9044955

Chiral Rh(II)-carboxylate catalysts have found widespread use in the field of metal carbene transformations, including asymmetric cyclopropanation reactions.1 Though several enantioselective transformations have been developed to date, little evidence is known
on how the chirality is projected near the reaction center by the chiral carboxylates. Davies et al. have suggested that four main possible symmetries have to be considered, from which only two
possess equivalent catalyst faces (Figure 1, C2 and D2).2 It has been postulated that catalysts having two different carbene-formation sites should not be effective in inducing enantioselectivity, since the more kinetically active and accessible face is apparently achiral (C1 andC4).

However, Fox et al. recently contradicted this concept by reporting the highly efficient asymmetric cyclopropanation of alkenes with R-alkyl-R-diazoesters using such a catalyst, where DFT calculations demonstrated that the all-up conformation of the catalyst plays a prominent role in these reactions.

All our experiments suggest that the halogenated rhodium carboxylate catalysts used in this process react through an all-up conformation, which is consistent with Fox’s DFT calculations made on non-halogenated analogues.

C-3 arylation of indole

Challenging chemical architectures of natural origin often point to gaps in synthetic methodology. For instance, there is a shortage of methods for C-3 quaternization of indoles with an aryl appendage. A number of natural products including haplophytine,1 bipleiophylline,2 hodgkinsine,3 and leptosin D4 (Fig. 1) contain a quaternary indole C-3 with an aryl appendage or a structure theoretically derived from such a motif as with haplophytine.1h Recent efforts by Nicolaou and co-workers,5 and Fukuyama and coworkers6 in the context of haplophytine have demonstrated the feasibility of the synthetic union of a substituted indole C-3 with an
aryl nucleophile,6 or a pseudo-aryl electrophile,5 however, both approaches were highly substrate specific and proceed in less than 25% yield.
In a much simpler context, Barton and co-workers have shown that treatment of skatole with tert-butyl tetramethylguanidine (BTMG) in the presence of 1.5 equiv of Ph4BiOTs results in
95% conversion to the C-3 disubstituted indolenine 1 (Fig. 2).7 This approach suffers from the required use of 4 equiv of aryl donor for each aryl group transfer. Additionally, extensive studies in these laboratories have shown that this bismuth mediated protocol does not have broad substrate scope and requires a tedious five-step reagent preparation.8

Baran reaported this method:
Tetrahedron 65 (2009) 3149–3154

The strategy has been generalized and performs well with a wide variety of substrate and reagent combinations. While this strategy is somewhat limited with respect to efficiency in appending very electron rich arene rings to C-3 of indole substrates, other than highly substrate dependent cases of Nicolaou5 and Fukuyama,6 there are no comparable methods in the
literature that allow for the direct C-3 quaternization of indoles with an arene ring.