4-Chloromagnesium chloride

Chloromagnesium chloride Sodium hydride Dilithium tetrachlorocuprate(II) 2,6-Dichlorobenzenethiol... 

The combination of metal tuning and double stereodifferentiation helps to prepare chelation and nonchelation products in the imine series7. In the case of an alkoxy substituent adjacent to the aldimino, the chelation product 10 is predominantly obtained with allylmagnesium chloride, chloromagnesium allyltriethylaluminate or allylzinc bromide, while the use of allyl-boronates or allyltitanium triisopropoxide, which lack the requisite Lewis acidity for chelation, gives 11 with good Cram selectivity. 

The results show that modest chelation control can be obtained using organomctallics like allylmagnesium chloride, chloromagnesium allyltriethylaluminate and allylzinc bromide, which are capable of /1-chelation. In contrast to this, 9-allyl-9-borabicyclo[3.3.1]nonane (9-allyl-BBN)... 

Similar yields can be obtained in this silylation by using the chloromagnesium salt (from butyl magnesium chloride) as described in Org. Synth. 1987, 6S, 61. 

The temperature reaches 15°C after 0.5 hr, and 20°C after 0.8 hr. Ethynylmagnesium halides can rapidly disproportionate to bis(chloromagnesium)-acetylene and acetylene at higher temperatures. It is important to maintain the reaction mixture at or below 20°C and to have an excess of acetylene in order to prevent formation of the bis(magnesium chloride). The checkers found that the ethynylmagnesium chloride can be formed at 10-15°C, thus minimizing the problem. 

The concentration of Grignard reagent could also be a factor in the stereochemical outcome. The addition of ethylmagnesium chloride to 26 in diethyl ether was highly selective for the R R stereoisomer at concentrations of 0.09-0.72 M (81-83%). The chloromagnesium compound is associated even at low concentrations. The stereoselectivity of addition to 26 by ethylmagnesium bromide, which is monomeric at low concentration, is concentration-dependent. Selectivity for the R R isomer varied from 74% at 0.70 M, where the dipolar model 28 should dominate, to 55% at 0.044 M, at which the cyclic model 27 should be more important. The stereoselectivity for reaction of 26 with ethylmagnesium iodide is also concentration-dependent. 

The best stereochemical results, however, were obtained with the new and bulky methylmetallic reagent, methyl triisopropoxy-titanium, (12) and with methylmagnesium chloride (eq. 13). Presumably, the more electrophilic chloromagnesium species formed a stronger complex with the bidendate enone sulfoxide than did the bromo or the lodomagnesium species (13) and thus forced the 3-addltlon to proceed entirely through the chelated and therefore locked conformation shown in model 9. 

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