Silyl Grignard reagents synthesis

The presence of the two spirotetrahydrofuran rings in these reactive intermediates is obviously not condudve to the stereocontrolled synthesis of 14. This problem was resolved by making recourse to 22, a precursor to 15, the silyl-protected (3-hydroxypropyl) substituent which was viewed to be sufficiently bulky to guarantee its equatorial occupancy in the lowest energy conformation (Scheme 3-4). Furthermore, treatment of 22 with Grignard reagent should be met with rapid deprotonation of the hydroxyl and formation of chelate 23. At this point, customary equatorial... 

Alkylation or acylation of ketones, sulfides, and amines. This reagent generally reacts with alcohols or carboxylic acids to form 2,2,2-trifluoroethyl ethers or esters in satisfactory yields, except in the case of alcohols prone to dehydration. The reaction of these ethers provides a simple synthesis of unsymmctrical sulfides (equation I). A similar reaction can be used for preparation of secondary amines or amides (equation II). Enolatc anions (generated from silyl cnol ethers with KF) can be alkylated or acylated with a or b (equation III). Use of Grignard reagents in this type of coupling results in mediocre yields. 

The C-7 side chain is introduced by addition of a Grignard reagent to the aldehyde generated from the primary hydroxyl function by oxidation, and subsequent Dess-Martin oxidation. The total synthesis is completed by conversion of the silyl-substituted furan into the maleic anhydride. The masked anhydride is liberated by successive photooxidation and further oxidation of the intermediate lactol with PCC [6a]. 

The acid or base elimination of a diastereoisomerically pure p-hydroxysilane, 1, (the Peterson olefination reaction4) provides one of the very best methods for the stereoselective formation of alkenes. Either the E- or Z-isomer may be prepared with excellent geometric selectivity from a single precursor (Scheme 1). The widespread use of the Peterson olefination reaction in synthesis has been limited, however, by the fact that there are few experimentally simple methods available for the formation of diastereoisomerically pure p-hydroxysilanes.56 One reliable route is the Cram controlled addition of nucleophiles to a-silyl ketones,6 but such an approach is complicated by difficulties in the preparation of (a-silylalkyl)lithium species or the corresponding Grignard reagents. These difficulties have been resolved by the development of a simple method for the preparation and reductive acylation of (a-chloroalkyl)silanes.7... 

Nitrosolysis of camphor ethyl acetal with ethanolic ethyl nitrite in sulphur dioxide yields the orthoester oxime (205) which is rapidly dehydrated by excess acetal to the orthoester nitrile which then reacts with sulphur dioxide to form the ester nitrile and diethyl sulphite.Further papers in this section include the full paper on ozonolysis of silyl ethers (Vol. 5, p. 33), another synthesis of camphor-enol trimethylsilyl ether (cf. Vol. 6, p. 41)/°° the conversion of camphor oxime with Grignard reagents into the corresponding imine with no aziridine formation/° the preparation of (206) by treating bornylene with trichloroacetyl isocyanate/ the oxidation of thiocam-phor to the 5-oxide and alkylation in the presence of thallium(i) ethoxide to a/S-unsaturated sulphoxides/ and the free-radical C-3 alkylation of camphor with alkenes. " ... 

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