Titanium-catalyzed hydroamination of 1,4-and 1,5-diynes by primary amines leads to imino-alkynes that undergo in situ 5-endo dig and 5-exo dig cyclization reactions, respectively. The products are 1,2,5-trisubsituted pyrroles accessed directly from readily available diyne starting materials.New synthetic strategies for the generation of substituted pyrroles are of continuous interest due to the ubiquity of this heterocycle in natural products and pharmaceuticals. 1 We have been exploring new reactions based on titaniumcatalyzed intermolecular hydroamination 2,3 using a selection of pyrrolyl-based ancillary ligands. In the course of previous studies, new protocols for the synthesis of hydrazones, indoles, 4,5 and R, -unsaturated iminoamines 6 have been discovered. In this paper, it is reported that the readily prepared, inexpensive titanium catalysts Ti(NMe 2 ) 2 (dpma) (A) and Ti(NMe 2 ) 2 (dmpm) (B) (Scheme 1) can be used in the monohydroamination of 1,4-and 1,5-diynes, which then undergo cyclization to the corresponding pyrroles. These pyrrole syntheses are an expansion of CuCl-catalyzed 1,3-diyne reactions with primary amines to generate similar products. 7 The pyrrolyl-based catalyst Ti(NMe 2 ) 2 (dpma) (A), 8,9 which has an X 2 L ancillary ligand 10 set (Scheme 1), has been examined for a variety of hydroamination applications by our group. The H 2 dpma ligand is prepared in a single step by a Mannich reaction between 2 equiv of pyrrole, 2 equiv of formaldehyde, and methylamine hydrochloride. 11 The most active catalyst known to date is the dipyrrolylmethane (1) For reviews see: (a) Gilchrist, T. L.

We conclude that there is no clear evidence that one technique or material has a substantial advantage over another for making complete dentures and removable partial dentures. Available evidence for the relative benefits of different denture fabrication techniques and final-impression materials is limited and is of low or very low quality. More high-quality RCTs are required.

Reaction of Ti(NMe2)4 with allyl alcohols and primary amines leads to the selective formation of secondary allylic amines. The allyl transfer from the alcohol to the amine occurs with selective allylic transposition. Due to substituent effects in the reactions, we postulate that the reaction occurs through a [2 + 2]/retro-[2 + 2]-cycloaddition mechanism. It was also found that a similar reaction could be accomplished with homoallylic alcohol. In this case, the more complex mechanism leads to the formation of 1-aza-spiro[5.5]undecane. Possible pathways for the homoallylic transfer and cyclization are discussed.

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Titanium-catalyzed hydroamination of 1,4-and 1,5-diynes by primary amines leads to imino-alkynes that undergo in situ 5-endo dig and 5-exo dig cyclization reactions, respectively. The products are 1,2,5-trisubsituted pyrroles accessed directly from readily available diyne starting materials.New synthetic strategies for the generation of substituted pyrroles are of continuous interest due to the ubiquity of this heterocycle in natural products and pharmaceuticals. 1 We have been exploring new reactions based on titaniumcatalyzed intermolecular hydroamination 2,3 using a selection of pyrrolyl-based ancillary ligands. In the course of previous studies, new protocols for the synthesis of hydrazones, indoles, 4,5 and R, -unsaturated iminoamines 6 have been discovered. In this paper, it is reported that the readily prepared, inexpensive titanium catalysts Ti(NMe 2 ) 2 (dpma) (A) and Ti(NMe 2 ) 2 (dmpm) (B) (Scheme 1) can be used in the monohydroamination of 1,4-and 1,5-diynes, which then undergo cyclization to the corresponding pyrroles. These pyrrole syntheses are an expansion of CuCl-catalyzed 1,3-diyne reactions with primary amines to generate similar products. 7The pyrrolyl-based catalyst Ti(NMe 2 ) 2 (dpma) (A), 8,9 which has an X 2 L ancillary ligand 10 set (Scheme 1), has been examined for a variety of hydroamination applications by our group. The H 2 dpma ligand is prepared in a single step by a Mannich reaction between 2 equiv of pyrrole, 2 equiv of formaldehyde, and methylamine hydrochloride. 11 The most active catalyst known to date is the dipyrrolylmethane (1) For reviews see: (a) Gilchrist, T. L.