Insertions trimethylsilyldiazomethane

Benzofurans. A method for the preparation of benzofurans from o-hydroxy phenones involves conversion to the alkynes (deoxygenation with one-carbon insertion) by reaction with lithiated trimethylsilyldiazomethane, and treatment of the products with TBAF. 

Alkylidenation-intramolecular insertion. A stereoselective synthesis of cyclo-pentenes from acyclic ketones occurs by reaction of the latter with lithio-trimethylsilyldiazomethane. An application of this method to the synthesis of (+)-cassiol and oxo-T-cadinoP attests to its usefulness. 

The thiol ester failed to provide the corresponding a-thio ketone when treated with diazomethane. No insertion was observed when ethyl diazoacetate (Et0C(0)CHN2) or trimethylsilyldiazomethane (Me3SiCHN2) were used with the selenol esters. 

A new two-step preparation of pyrroles from (3-amino ketones and trimethylsilyldiazo-methane was developed by Aoyama and Shioiri <97SL1063>. Treatment of the N-substituted (5-amino ketones 15 with lithium trimethylsilyldiazomethane affords the alkylidene carbene intermediates 16 which undergo intramolecular insertion to yield the 2-pyrrolines 17. In this instance, dehydrogenation to the corresponding pyrroles was accomplished using Mn02-... 

Insertion Reactions. Trimethylsilyldiazomethane undergoes net insertion between the B-C bond of borinate and boronate esters. Thus, olefin hydroboration, followed by treatment with TMSCHN2, oxidation, and desilylation offers a method for hydroxymethylation of alkenes in fair to moderate yield (eq 54). Stable, chiral allenylboranes (IR and IS) are prepared by reaction of TMSCHN2 with 5-MeO-9-BBN followed by resolution with pseudoephedrine and reaction with allenyl magnesium bromide (eq 55). Compounds IR and IS are useful for the asymmetric allenylboration of aldehydes with predictable absolute stereochemistry. The precursors to 1 are then readily recovered during work-up. ... 

Lithium trimethylsilyldiazomethane has proved particularly useful in the conversion of ketones into alkylidene carbenes, vide supra, that readily undergo 1,5 C-H insertion reactions to afford cyclopentenes (eq 56). Yields are generally good and the chemoselectivity of C-H insertion is predictable. The C-H insertion of the singlet carbene into heteroatom-bearing stereocenters proceeds with retention of stereochemistry (eqs 57 and 58). Reaction with acetals affords spiroketals (eq 59) or 2-cyclopentenones after acetal hydrolysis (eq 60). ... 

When borane BH3 was reacted with 2 equiv. of trimethylsilyldiazomethane (TDM), insertion of TDM into B-H with release of N2 occurred to give tris(trimethylsilylmethyl)borane in a high yield [69] (Scheme 46). However, addition of an excess of TDM to borane did not lead to polymerization of TDM. 

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