The article contains sections titled: 1. Introduction 2. Fundamental Synthetic Routes for Organosilicon Compounds 2.1. Direct Synthesis of Organohalosilanes 2.2. Grignard Synthesis 2.3. Syntheses with Alkali Metals 2.4. Addition Reactions (Hydrosilylation) 2.5. Substitution Reactions of Si−H Bonds 2.6. Coproportionation and Disproportionation 3. Silicon‐Functional Organosilicon Compounds 3.1. Halo‐ and Pseudohalosilanes 3.2. Alkoxy‐ and Aryloxysilanes 3.3. Acyloxysilanes 3.4. Oximino‐ and Aminoxysilanes 3.4.1. (Alkylamino)alkylsilanes 3.5. Organofunctional Organosilicon Compounds 4. Vinyl and Other Alkenyl Compounds 4.1. Organohalogenated Compounds 4.2. Nitrogen‐Containing Compounds 4.3. Cyanoalkyl Compounds 4.3.1. Organic Amino Compounds 4.3.2. Other Nitrogen Compounds 4.3.3. Organosulfur Compounds 4.4. Mercapto and Sulfidic Organofunctions 4.4.1. Compounds Containing Sulfur ‐ Oxygen Groups 4.4.2. Oxygen‐Containing Compounds 4.5. Epoxy and Other Oxy Compounds 4.5.1. Acrylates and Other Ester Functions 4.5.2. Acid Anhydrides and Other Carboxy Groups 4.5.3. Other Organofunctions 4.6. Other Organosilanes 5. Tetraorganosilanes 5.1. Production 5.1. Polysilanes 5.2. Uses 6. Silylating Agents 6.1. Silanes as Protecting Groups 6.1. Organosilicon Pharmaceuticals 6.1. Silanes for Modification of Organic Polymers 6.1.1. Cross‐Linking of Polyethylene 6.1.1. Donor Silanes 6.2. Silane Coupling Agents 6.2.1. Mode of Action 6.3. Analysis 6.4. Toxicology and Environmental Aspects 7. Economic Aspects 8. References

with difficulty. We report here a versatile synthetic pathway leading to syn-benzene dioxides and their dioxocin valence tautomers via a Diels-Alder route. trans,trans-l,3-Butadienylene diacetate 3, a valuable diene component for the synthesis of natural products with highly oxygenated cyclohexane-frameworks via DielsAlder routes ['], reacts with excess propiolaldehyde to give the adduct 4 (m. p. = 79-80 "C, 89%). Os0,-catalyzed oxidation of 4 with hydrogen peroxide (cf. Scheme A) leads to cis-hydroxylation of the 4,5-double bond to give a diol, to which, based on the assumption that the attack of the oxidant occurs from the sterically more favorable side of the ring, we assign the structure 5 (m.p.= 174-175 "C, 60%). Attempts to convert the bismesylate 6 (decomp. 167 "C, 71%) of the diol 5 with KOH in aqueous methanol into the syn-benzene dioxide lg afforded aromatic products-presumably as a result of an initial attack of the base at the conjugated double bond in the sense of a Michael reaction. As an alternative, the acid 7, instead of the aldehyde 6 (Scheme A), or the corresponding alcohol and its isomer 8, respectively (Scheme B), can be treated with base. 6 can best be oxidized to 7 (decomp. 189 "C, 92%) using Jones' reagent. Treatment of 7 with base yields, as uniform product, the syn-benzene dioxide carboxylic acid Id (m. p. = 145-146 "C, 81%). The dominance of the epoxide ring closure in 7 can be attributed to formation of the carboxylate, which suppresses nucleophilic additions to the double bond. In refluxing tetrachloromethane Id isomerizes almost completely within 24 h to 1,4-dioxocin-6-carboxylic acid 2d (m.p.=93-94"C). Heating either Id or 2d in methanol leads to an equilibrium mixture containing the valence tautomers in the ratio 32 :68.Derivatization of the acid 2d to the methyl ester or amide can advantageously be carried out via the acid chloride 2e, prepared by means of sulfinyl chloride, since this can readily be isolated as a uniform valence tautomer upon recrystallization (m. p. = 32 "C, 9oyo). Contrary to expectations, reduction of the aldehyde 6 with NaBH, does not afford the corresponding alcohol, but-via an acyl migration which does not influence the synthetic concept-the isomeric alcohol 8 (m. p. = 109-110 "C, 75%). This rearrangement apparently proceeds from the alcohoIate, which is formed by attack of a hydride ion at the aldehyde function in 6. As suggested by the behavior of 7, treatment of 8 with base also leads smoothly to epoxide ring-closure ; moreover, the primary OAc group is hydrolyzed, so that If is isolated as the reaction product (m. p. = 93 "C, 60%). If is readily oxidized by Mn02 to l g (m.p.=4O0C, 50%). Finally, heating lg in acetone leads quantitatively to the relatively volatile 1,4-dioxin-6-carbaldehyde 2g, which was proved to be a uniform valence tautomer by NMR spectroscopy (short path distillation, 70 "C bath temp. 0.2 torr, 94%).2e and 2g are attractive starting materials for the synthesis of the natural product LL-Z1220 lc. The complex 5 , whose structure has be...

No abstract

AbstractThe cationic carbyne complex [(CO)5WCNEt2]BF4 (1) reacts with potassiumdiphenylamide, KNPh2, with nucleophilic addition of the amide anion to give (CO)5W[C(NEt2)NPh2] (2). The corresponding reactions with KPPh2, KPEt2, KPMePh, NaSbPh2 and NaBiPh2 yield the complex [(CO)5W(CNEt2)]2 (3), which is formed by reductive dimerization of two carbyne fragments. In case of KPMePh the carbene complexes (CO)5W[C(NEt2)PMePh (4) and trans-(MePhPH)(CO)4W[C(NEt2)PMePh] (5) are also obtained. On warming in solution 5 spontaneously rearranges to the novel cyclic carbene complex (6). Reaction conditions, properties and spectroscopic data of the new compounds are reported.

References[l] W. Wagemann, M. Iyoda, H.M. Deqer, 3. Sombroek, and E. Vogel, Anqew. Chem. 90 ( 1 9 7 8 ) 9 8 8 : Angew. Chem.internat. Ed. Engl. 17 ( 1 9 7 8 ) 956.