Variable Strategy Toward Carbasugars and Relatives. Part 1. Stereocontrolled Synthesis of Pseudo‐β‐D‐gulopyranose, Pseudo‐β‐D‐xylofuranose, (Pseudo‐β‐D‐gulopyranosyl)amine, and (Pseudo‐β‐D‐xylofuranosyl)amine.